Color Analysis in 

Air Traffic Control 

Displays, Part I. 

Radar Displays

Jing Xing

Civil Aerospace Medical Institute

Federal Aviation Administration

Oklahoma City, OK 73125

October 2006

Final Report

DOT/FAA/AM-06/22

Office of Aerospace Medicine

Washington, DC 20591
NOTICE

This document is disseminated under the sponsorship 

of the U.S. Department of Transportation in the interest 

of information exchange. The United States Government 

assumes no liability for the contents thereof.

___________

This publication and all Office of Aerospace Medicine technical reports are 

available in full-text from the Civil Aerospace Medical Institute’s publications 

Web site: 

www.faa.gov/library/reports/medical/oamtechreports/index.cfm
i

Technical Report Documentation Page 

1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. 

DOT/FAA/AM-06/22 

4. Title and Subtitle 5. Report Date 

Color Analysis in Air Traffic Control Displays, Part I. Radar Displays October 2006 

6. Performing Organization Code 

 

7. Author(s) 8. Performing Organization Report No. 

Xing J 

9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) 

FAA Civil Aerospace Medical Institute 

P.O. Box 25082 11. Contract or Grant No. 

Oklahoma City, OK 73125 

12. Sponsoring Agency name and Address 13. Type of Report and Period Covered 

Office of Aerospace Medicine 

Federal Aviation Administration 

800 Independence Ave., S.W. 

Washington, DC 20591 14. Sponsoring Agency Code 

15. Supplemental Notes 

Work was accomplished under approved task AM-HRRD522 

16. Abstract 

One of the current trends in air traffic control (ATC) display technology is a substantial increase in the use of 

color. Whereas the advantages of color may seem apparent, little attention has been devoted to potential 

disadvantages of color use with respect to complex cognitive aspects of the ATC environment. Although 

controllers use several different displays simultaneously (designed and manufactured by different companies), the 

Federal Aviation Administration (FAA) has not yet adopted a standard for color use to ensure that the various 

color schemes are compatible. At present, there is no systematic documentation and analysis of color use in ATC 

displays. This lack of standardization and documentation presents a challenge for manufacturers to design 

compatible color schemes and for the FAA to evaluate the effectiveness of a display at acquisition. This report 

was designed to address the lack of such information. The study evaluates color-coding, color usage, task 

purposes and effectiveness of color use, potential shortcomings, and color complexity for three types of radar 

displays used by operational controllers. This systematic documentation allowed us to assess compatibility across 

displays. The study also revealed some visual factors that may affect the usefulness of a display. The results of 

these investigations will be beneficial for the development of design prototypes and for acquisition evaluation of 

new ATC display technologies. 

 

17. Key Words 18. Distribution Statement 

 

 

Color, Evaluation, Air Traffic Control, Displays, Interface Document is available to the public through the 

Defense Technical Information Center, Ft. Belvior, VA 

22060; and the National Technical Information 

Service, Springfield, VA 22161 

19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price 

Unclassified Unclassified 21 

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized 

iii

ACKNOWLEDGMENTS

We sincerely thank Drs. Pam Della Rocco and Mike McAnulty for their coordinating the data collection of this study at the FAA William J. Hughes Technical Center. This project could not be done without 

their help. Dr. Della Rocco proposed the method of documenting color use in ATC displays. We thank 

Ben Williems and Kenneth Allendoerfer for their assistance in data collection. We also express our appreciation for the support from the following ATC facilities: ZDC, ZNY, ZNC, PHL tower, DCA tower, 

SFO tower, New York TRACON, Potomac TRACON and PHL TRACON. We appreciate the effort of 

all the FAA reviewers and editors whose efforts greatly improved this report.

v

Contents

INTRODUCTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

METHODS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Data Collection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Color Analysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Color Specification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

RESULTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Color Analysis for Individual ATC Displays. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Comparisons of Color Use in ATC Displays. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

DISCUSSION AND CONCLUSIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Operational Effects of Drawbacks of Color Use in ATC Displays. . . . . . . . . . . . . . . . . . . . . 12

Limitations of the Analysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

CONCLUSIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

REFERENCES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

APPENDIX A. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-1

APPENDIX B. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-1

APPENDIX C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-1

1

Color Analysis in Air Traffic Control Displays, Part I. Radar Displays

INTRODUCTION

As a result of introducing new technologies into the 

air traffic control (ATC) system, computer displays have 

become one of the major sources for air traffic controllers 

to acquire information and control traffic. Since current 

display technologies make it easy to render colors on computer monitors, one of the changes in ATC technologies 

during the past decade is the increasing use of color. At 

present, the Federal Aviation Administration (FAA) has 

no requirements on the use of color in ATC displays. 

Hence, manufacturers of ATC technologies create their 

own color schemes for their displays or customize display 

colors to suit their users. These situations raise a number 

of issues related to the use of color, two of which are addressed in this report. 

The first issue pertains to the advantages and drawbacks 

of color use in individual displays. While the advantages 

of color seem to be apparent, many display designs do not 

ensure the advantages of color use in the ATC environment. Moreover, little attention has been paid to potential drawbacks of color use. Xing (2006a) studied color 

use in a number of ATC facilities and identified several 

color factors that had the potential to negatively affect 

task performance. The author developed two checklists 

to evaluate the effectiveness and drawbacks of color use 

in ATC displays. These checklists provide a means to 

systematically evaluate color use across displays. 

The second issue is a paradox in ATC technologies: 

Different manufacturers design the color schemes of 

individual ATC displays, and they use colors in a display 

for the benefit of the display in stand-alone conditions. 

However, most controllers use several displays at their 

workstation. This report includes displays used at two 

types of air traffic facilities: the en route air traffic control 

center, referenced as en route facilities, and the terminal 

radar approach control, referenced as TRACON facilities. Typically, a controller uses a primary radar display 

to monitor and control aircraft and one or several 

auxiliary displays to acquire additional information for 

decision-making. For example, operational controllers 

at some en route facilities use Display System Replacement (DSR) as the primary display; they also use User 

Request Evaluation Tool (URET), which is placed next 

to the DSR, to acquire information such as flight status 

or route. These displays use color to encode information. 

However, since the color schemes on these displays were 

developed independently, without respect to each other, 

color usages can be incompatible between displays. Such 

incompatibility increases controllers’ mental workload 

and reduces the usefulness of displays. Cardosi (2003) 

pointed out that compatibility between displays of ATC 

tools was crucial for controllers to adapt to the tools. 

Therefore, it is desirable for the FAA and manufacturers 

to have the proper methods and information resources 

to ensure display color compatibility. 

This study was intended to achieve two goals: 1) to 

analyze the benefits and drawbacks of color use in some 

most frequently used ATC displays; and 2) to provide a 

systematic documentation of color use in primary ATC 

displays. We first chose to study three primary radar 

displays for operational controllers to manage aircraft: 

Automated Radar Terminal System (ARTS) Color Display 

(ACD), Standard Terminal Automation Replacement System (STARS), and Display System Replacement (DSR). 

A companion report was focused on auxiliary displays. 

For each display, this report presents information about 

color usage, the effectiveness of color use for given tasks, 

the potential drawbacks of color use, and the overall color 

complexity of the display. 

METHODS 

Data Collection

Data about color usage were collected from the displays 

provided by the FAA William J. Hughes Technical Center. 

The displays were identical to those currently used in 

ATC facilities. Color usage and the associated tasks were 

documented for each display. Because ATC displays were 

complex and a single display usually had multiple display 

modes, we documented color usages by the functional 

components of a display. A spreadsheet was used for 

data collection in which the elements along the rows of 

the spreadsheet were the functional components such as 

background, menus, lists, datablock (text, target, flashing, 

highlighting, fly-out window), geographic information 

(boundaries, maps, compass, range rings, etc), weather, 

and graphic tools; and the elements along the columns 

were color specification, usage, purpose, redundant cues, 

and subjective opinions about the efficiency of color use 

on task performance.
2

Color Analysis

In a previous study, Xing (2006a) developed two 

checklists to assess color use in ATC displays. The first 

checklist, shown in Appendix A, assesses the effectiveness of color. The second checklist, shown in Appendix 

B, assesses the drawbacks of color use. This study utilizes 

those checklists to analyze color. 

Purposes of Color Use in ATC Displays

To use the checklists, we first needed to determine the 

purposes of color use. Xing (2006b) identified three main 

task purposes of color use in ATC displays:

1. Color is used to capture attention. Salient colors are 

often chosen to encode information that needs to be 

attended to immediately, such as an alert or emergency.

2. Color is used to identify certain types of information 

so that searching for the information in complex 

scenes can be accomplished more effectively. In this 

application, each color has a distinctive meaning. 

3. Colors are used to segment complex scenes in a display 

so that information belonging to the same category 

can be organized together. In this application, color 

is not associated with specific meanings. 

Therefore, we referred to the task purposes of color use 

in three terms throughout this report: Attention, Identification, and Segmentation. In addition to these purposes, 

each display has a background color and one or several 

“default” colors that are used to depict information in its 

normal status. These colors are not associated with any 

task purposes and do not have any meanings. 

The Checklist for the Effectiveness of Color Use

For each task purpose, the first checklist contains 

several factors that determine the effectiveness of color. 

The key factors are:

1. The effectiveness of color for attention is mainly determined by the luminance and chromaticity differences 

between the color target (to be attended to) and other 

materials within the view field (Treisman & Gelade, 

1980; Nagy & Sanchez, 1992);

2. Identification is mainly determined by the chromaticity differences between the colors and how well the 

colors can be named reliably (Smallman & Boynton, 

1990; Boynton, MacLaury, & Uchikawa, 1989); 

3. Segmentation is determined by the uniformity of areas 

to be segmented and the luminance or chromaticity 

differences between the areas (Nothdurft, 1993; McIlhagga, Hine, Cole, & Snyder, 1990);

4. The effectiveness of color for any of the three task 

purposes decreases with the increase of the number 

of colors (Carter, 1982). 

We classified the effectiveness of color use into three 

categories: “E,” effective for the given task purpose; “NE,” 

not effective for the task purpose; and “D,” effectiveness of 

color use depends on other visual attributes. For example, 

a circle filled with red may or may not be salient enough 

to draw attention in a colorful complex scene, depending on the size of the circle relative to the sizes of other 

materials in the scene (Treisman & Souther, 1985). 

The Checklist for Potential Negative Effects of Color 

Use

The second checklist contains the following factors 

that can negatively affect task performance:

Distraction: Multiple colored targets that need attention are onset simultaneously within the visual field 

(Simons & Chabris, 1999; DiVita, Obermayer, Nugent, 

& Linville, 2004).

Coding uncertainty: Messages (text or symbols) 

identified by colors do not have a unique meaning in 

identification tasks; thus, color cannot serve as the selection criteria for identification (Jeffrey & Beck, 1972; 

Green & Swets, 1988).

Loss of integration: Messages in different colors need 

to be considered together simultaneously for successful 

task performance (Gegenfurtner, 2004).

Multiple color schemes: 1) One color is used for 

multiple purposes, or 2) multiple colors represent the 

same meaning (Poulton & Edwards, 1977). 

Experience interference: Color use is against controllers’ experience. Typical cases include: 1) red, bright yellow, 

or orange-red are used to represent non-critical information; 2) dark colors such as black, purple, or brown are 

used for critical information; 3) green is used to represent 

specific meanings rather than just indicating messages of 

normal status; and 4) use of a bright background color 

(Cohen, Dunbar, & McClelland, 1990; Virzi & Egeth 

1985; Cardosi & Hannon, 1999).

Text readability: The luminance contrast between text 

and background colors is less than the threshold contrast 

(typically taken as 20%) for error-free reading (Legge, 

Rubin, & Luebker, 1987; Scharff & Ahumada, 2002).

The factors listed above were used to evaluate each 

use of color. The potential consequences of these factors 

on task performance can be found in Appendix B. The 

six factors were examined for each color usage and the 

results were classified as either “Y” or “No.” “Y” means 

that the drawback factor exists; thus, the use of this color 

has the potential of negatively affecting task performance. 

“No” means that the factor does not exist for the given 
3

color usage; thus, the use of this color does not have the 

potential of negatively affecting task performance. 

Documentation of display-wide color usages

In addition to the analysis of individual color usages, 

we also documented two aspects of the overall color 

use in a display: default colors and color complexity. A 

default color is the one used to depict information in a 

normal status and is not associated with any particular 

task. The typical default colors in computer displays are 

white, black, and green. Color complexity is assessed 

with three indices: 

1. The total number of colors in the display (excluding 

the background color). For simplification, only the 

colors differing in chromaticity are counted; in other 

words, if two colors have the same chromaticity but 

different luminance, they are counted as one color; 

2. The total number of colors used for identification; 

3. The number of sets of color-coding, where each 

set of colors is used to identify different aspects of 

information. 

Since effectiveness is inversely correlated with complexity, the complexity indices reflect the overall effectiveness 

of color use (Xing, 2006a). Cummings, Tsonis, and Xing 

(2006) demonstrated that the percentage of performance 

errors rose if the number of colors used for identification 

was more than six; while another study indicated that 

color did not help task performance when more than 

three sets of color-coding were used in a visual display 

(Yuditsky, Sollenberger, Della Rocco, Friedman-Berg, & 

Manning, 2002).

Color Specification

To compute the effectiveness of a color for a given task 

purpose, we need to determine the luminance and chromaticity specifications of the color. A computer monitor 

generates a color through three phosphor channels: red, 

green, and blue. The amount of phosphors emitted from 

a channel is specified with three digital values: r, g, and b

for red, green, and blue phosphors, respectively. Computer 

programmers use these three numbers, typically denoted 

as rgb values, to specify a color on a display.

While rgb values specify the physical attributes of 

displayed color, they do not describe how users perceive 

the color. To describe human color perception, the International Commission on Illumination (CIE) defined 

color chromaticity coordinates. In this definition, a color 

can be specified by three variables: x,y, and L, where x and 

y determine the chromaticity, while L is the luminance 

of a color. The x and y coordinates can vary between 0 

and 1. The xyL values of a color can be measured with a 

colorimeter. When measurements are not available, these 

values can be computed from rgb values. The transformations from rgb to xyL values are described in Appendix C. 

The chromaticity difference, denoted as delta C, between 

two colors (specified by x1 y1 and x2 y2) can be computed 

as Delta C = sqrt((x1 -x2)

2

 + (y1 - y2)

2

 ).

RESULTS

This section includes two parts: The first describes the 

color documentation and analysis for each ATC display. 

We briefly describe color usages in every functional component, point out the situations where color use was not 

effective or had potential drawbacks, and analyzed color 

complexity. The results for each display were presented 

in a summary table. The second part describes some 

comparisons of color use across displays. 

Color Analysis for Individual ATC Displays

ARTS Color Display (ACD) 

ACD is a primary radar display used at TRACON 

facilities. ACD contains a traffic situation area occupying 

the majority of the computer screen and a menu bar on 

the top of the screen. The traffic situation area graphically displays aircraft position symbols and datablocks 

superimposed on maps, weather, and range rings. 

The components of ACD are the background, menus, 

datablock, range ring, maps, aircraft symbol, and weather. 

We identified color usage for every component and analyzed their effectiveness as well as drawbacks. The results 

are presented in Table 1. The order of the elements in 

the table (from left to right) is components, color, color 

usage, task purpose, effectiveness, and six drawback factors. The display-wide information about color use in 

ACD, listed in the bottom portion of Table 1, includes 

default colors and the three metrics of color complexity 

(i.e., sets of color-coding, number of colors, and number 

of color uses). 

Below we describe the evaluation results of the color 

analysis of the ACD. To avoid tedious descriptions, we 

only focused on the results where the effectiveness of 

color use was estimated as “NE” (not effective for the task 

purpose), or “D” (effectiveness of color use depends on 

other visual attributes), and where the drawback factors 

were identified as “Y,” indicating there is at least one 

drawback to the use of color. 

Background

Controllers can adjust the background color of the 

screen for their preference from completely dark to 60% 

blue. However, most controllers set their screen at a very 
4

dark color. The background color is not associated with 

any task purpose. 

Datablock

A datablock is composed of several short lines of 

text. Four colors are used to encode the datablock text. 

Normal (unowned) datablocks are green. Datablocks for 

owned aircraft (those that are the responsibility of the 

controller) are white. A datablock in a pointout status 

is yellow. A controller uses pointouts to identify targets 

of interest to other controllers. When an aircraft is in 

a potential collision or conflict situation (with another 

aircraft or the ground), the red alert text “CA” (Collision Alert) or “LA” (Low Altitude Alert) appears on top 

of the aircraft’s datablock. The alert text blinks until the 

controller acknowledges it. The red text remains until 

the conflict is resolved. 

Among the datablock colors, white is used to segment 

datablocks from those in green. It has two potential 

drawbacks: distraction and loss of integration. Since white 

datablocks are much brighter than green datablocks, they 

automatically draw controllers’ attention, which reduces 

controllers’ perception of datablocks in other colors. 

Moreover, green and white colors segregate the owned and 

unowned aircraft in a controller’s mental representation of 

the traffic situation. Thus, the integration between owned 

and unowned aircraft is reduced. However, controllers 

need to consider owned and unowned aircraft together 

to ensure aircraft separation. This is especially important 

for those aircraft near sector boundaries. Due to the 

difference in the colors, controllers may be less likely to 

detect conflicts between owned and unowned aircraft. 

Therefore, application of white color to owned datablocks 

has the potential to cause operational errors. 

The red text “CA” or “LA” on the top of a datablock 

is intended to capture controllers’ immediate attention. 

However, red text is less effective in drawing attention 

because its luminance is much lower than that of the 

white and green datablocks. Controllers tend to rely on 

the blinking signal rather than the color signal to detect 

the alerts. The red text is also used to identify conflicting 

datablocks after blinking has stopped. While red is effective to identify datablocks from those in white, green, and 

yellow, it results in low text readability. The luminance 

contrast between the red text and black background is 

about 10%. Many visual studies have demonstrated that 

the luminance contrast for effortless, error-free text reading 

should be at least 20% (e.g., Legge et al., 1987). 

Menus

The menu bar is located at the top of the screen. It 

contains a number of text buttons. The background color 

of the text buttons is gray-blue. Thus, one can easily segment the menu area from the rest of the display. The text 

is green. The only problem associated with the color use 

is that the text readability is low. The luminance contrast 

between green text and the gray-blue background is about 

15%. However, since each button has the fixed text at 

the fixed location, controllers can locate a particular 

button by remembering the location rather than reading 

the text, but it takes time and mental resources to learn 

the location.

Aircraft symbol 

The current position of an aircraft is displayed on the 

ACD with a small graphic symbol. There are two types 

of symbols: target, denoted to an aircraft that is detected 

by radar; and beacon, denoted as an aircraft whose position is predicted from the flight plan. All the symbols 

have the same shape but different colors: slate blue for 

targets and green for beacons. In addition, the symbol of 

an aircraft that is currently being scanned by the radar is 

indicated with dark sky blue. While these colors are used 

for identification, the chromaticity difference between 

slate blue and dark sky blue is less than the threshold 

for effective identification (i.e., users cannot reliably and 

rapidly identify the information by color). Therefore, 

they are not effective for the identification purpose. The 

history trails of aircraft symbols are royal blue. This color 

is used for the purpose of segmentation. 

Weather

Weather information is represented by filled background areas and overlays with datablocks, aircraft symbols, and range rings. ACD provides six weather levels: 

Levels 1,2 for moderate weather; Levels 3,4 for heavy 

weather, and Levels 5,6 for severe weather. It is crucial 

for controllers to distinguish different weather levels. 

Weather levels are represented by both colors and shades. 

Levels 1,2 are gray, Levels 3,4 are orange, and Levels 5,6 

are orange-red. An area with weather Levels 1, 3, or 5 is 

uniformly filled with the corresponding color, while levels 

2, 4, or 6 are depicted by the respective colors with the 

stipple addition. It is desirable for controllers to immediately notice heavy / severe weather to make decisions. 

Thus, orange and orange-red are used to draw attention 

and to identify weather levels.

The luminance of orange-red is lower than the luminance of the datablocks; thus, the color signal itself is not 

adequate to draw attention. In this case, the effectiveness 

of the color depends on the size of the filled area. Only 

when the orange-red area is comparable to or significantly 

larger than the area of individual datablocks can it be 

salient enough to draw attention. Otherwise it will not 
5

pop out from other displayed materials. The same analysis 

applies to orange color for weather levels 3 and 4. 

The text readability of datablocks on a filled area of 

weather can become very low given that the text and 

background colors of white vs. gray, red vs. orange, and 

red vs. orange-red are all below the threshold contrast (i.e., 

20%) for error-free reading. Therefore, if an aircraft flies 

into a heavy weather area, controllers may find it difficult 

to read the datablock. However, controllers have to be 

able to read the information in the datablocks, as aircraft 

information may change more rapidly than weather. 

Display-wide information

The display-wide information about color use in ACD 

is shown in the bottom portion of Table 1. The default 

color is green. Three sets of colors are used for identification tasks in which controllers have to remember the 

meaning of colors. Those are (gray, orange, orange-red) 

for weather levels, (green, slate blue, dark-sky blue) for 

aircraft symbols, and (white, yellow, red) for datablocks. 

When counting the number of colors, we only considered 

those varying in chromaticity but not in luminance. For 

instance, a dark green and a light green were counted as 

one color as long as they had the same chromaticity. Also, 

the background color of the display was not counted. 

Finally, the total number of color uses is 14 while the 

total number of colors is 12. The difference between 

the number of color uses and total number of colors 

indicates that some colors are used more than once to 

represent different types of information. For example, 

green is used in the menu, datablock, and some aircraft 

symbol components.

Standard Terminal Automation Replacement System 

(STARS)

STARS is also a primary display used in terminal facilities. The basic layout of a STARS display has the same 

format as that of ACD; however, STARS has more display 

components. The menu bars, system status alert, and 

coordination list are located along the top and left edges 

of the STARS display. The traffic situation area shows 

datablocks, aircraft symbols, geometric graph (maps, 

range rings, compass, and predicted track line), weather, 

and geographic restriction areas. Color is essentially used 

in every component. We presented the results of color 

analysis for STARS in Table 2 (formatted like Table 1). 

Below we described the situations where color use was 

either not effective for a given task or had potential to 

negatively affect task performance.

Toolbar (menu bars)

The menu bars of STARS use nine colors. The 

background color of the menu bars is gray-green. It 

segments the menu area from the traffic situation area. 

The background color of the text buttons on the menu 

bars is dark green. The color differentiates buttons from 

the background of menu bars. When a button is selected, 

its background color becomes “selected dark green,” 

which has the same chromaticity as the dark green but 

a higher luminance. The default color for menu text is 

white. Highlighted text is displayed in bright yellow. 

The purpose of the highlighted yellow is to draw attention. However, yellow has a lower luminance than 

white; therefore, yellow is not effective to draw attention 

away from white text. Blue-gray and selected blue-gray 

are used to identify the different status of weather level 

selections. However, the luminance difference between 

the two colors is not effective as a selection criterion for 

identification. Finally, most of the colors in the menu bars 

have a common drawback factor: They are used more 

than once to represent different types of information in 

STARS, as described later.

System status alert 

The system status alert is a text box in the menu area. 

Within the box are text fields for system failure alert, system 

overload alert, and radar failure alert. The background 

of the box is black. If an alert is issued, red alert text appears in the corresponding field of the box. Red is used 

to draw the controller’s attention to the alert. However, 

red text is not salient enough to draw attention because 

of its low luminance. In addition, the luminance contrast 

of the red text on the black background is less than the 

threshold contrast for error-free reading.

Lists

STARS provides controllers with a number of lists 

containing various types of traffic information. The lists 

can be displayed by clicking the buttons in menu bars. 

The titles of the lists are blue-gray, the same color used 

for the weather selection buttons on the menu bars. 

Also, the luminance contrast of the blue-gray text on 

the black background is below the threshold contrast 

for error-free reading.

Coordination list

The coordination list provides information about the 

coordination status between controllers. The list uses three 

colors to indicate the status of coordination texts: white 

for unsent messages, green for acknowledged messages, 

and yellow for unacknowledged messages. The purpose 

of these colors is identification. A drawback is that these 

colors are also used to represent other information on 

STARS. 
6

Table 1: Color Documentation and Analysis for ARTS Color Display (ACD) 

These symbols in Tables 1-3 represent the longer words: 

dis ̛ distraction unc ̛ coding uncertainty int ̛ loss of integration 

mul ̛ multiple color schemes exp ̛ experience interference read ̛ text readability 

Att ̛ Attention Iden ̛ Identification Seg ̛ Segmentation 

Eff ̛ Effectiveness E ̛ Equally effective NE ̛ Not effective 

NA ̛ Not Applicaple D ̛ The effectiveness of color 

depends on other factors 

Y ̛ Yes 

Component Color Usage Purpose Eff Drawback factors 

Dis Unc Int Mul Exp Read

Background Black / 

blue

Filled

screen 

NA NA NA NA NA NA No NA 

Background GrayblueText

box

Menus Seg E No No No No No NA 

Text Green Text Default NA No No No No No Y 

Unowned Green Text Default NA No No No No No No 

Owned White Text Seg E 

Iden E 

Y No Y No No No 

Point-out Yellow Text Iden E Y No Y No No No 

Att NE 

Datablock 

Alert Red Text 

Iden E 

No No No No No Y 

Range rings Gray Curve Seg. E No No No No No No 

Maps Wheat Line seg E No No No No No No 

Beacon Green Shape Iden E No No No Y No No 

Target Slate 

blue

Shape Iden NE No No No Y No NA 

Current 

scans 

Darksky blue Shape Iden NE No No No Y No NA 

Aircraft 

symbol

History 

trail

Royal 

blue

Shape Seg E No No No No No NA 

Levels

1,2

Gray Filled 

area

Iden E No No No No No Y 

Levels Iden E 

3,4

Orange Filled 

area Att D 

No No No No No Y 

Iden E 

Weather 

Levels

5,6

OrangeredFilled

area Att D 

No No No No No Y 

Stipple Gray Dot Seg E No No No No No NA 

Default colors Green 

Sets of color-coding (White, Yellow, Red) for datablocks 

(Green, Slate blue, Dark-sky blue) for aircraft symbols 

(Gray, Orange, Orange-red) for weather levels 

Number of colors 12 

Number of color 

usages 

14
7

Table 2: Color Documentation and Analysis for Standard Terminal Automation Replacement System (STARS) 

Component Color Usage Purpose Eff Drawback factors 

Dis Unc Int Mul Exp Read 

Background Dim gray 

/black

Filled

screen

NA NA NA NA NA NA No NA 

Background Gray green Filled 

area

Seg E No No No Y No NA 

Button

background 

Dark green Filled 

box 

Seg E No No No Y No NA 

Selected

background 

Selected

dark green 

Filled

box 

Seg E No No No Y No NA 

Button

shadow top 

Dark

gray 

Filled

area

NA NA NA NA NA NA No NA 

Button

shadow 

bottom

Black Filled 

area

NA NA NA NA NA NA No NA 

Normal

text 

White Text Default NA No No No Y No No 

Highlight 

text 

Bright

yellow 

Text Att NE No No No Y No No 

WX available 

& site 

unavailable 

Blue-gray Filled 

box 

Iden NE No No No Y No No 

Toolbar 

(Menu bar) 

WX selected Selected 

blue-gray 

Filled

box 

Iden NE No No No Y No No 

System status alert Red Text Att NE No No No No No Y 

System status weather Cyan Text Iden E No No No No No No 

Lists Title Blue-gray Text Seg E No No No Y No Y 

text Green Text Default NA No No No No No No 

Unsent White Text Iden E No No No Y No No 

Acknowledged Green Text Iden E No No No Y No No 

Coordination 

list

Unacknowledged Yellow Text Iden E No No No Y No No 

Background Beige Filled 

area

Geographic Seg E No No No No No NA 

restriction Area 

Text Green Text Default NA No No No No No Y 

Normal Green Text Default NA No No No No No No 

Highlighten White Text Seg E No No No No No No 

Att NE 

Datablock

Alert Red Text 

Iden E 

No No No No No Y 

Range rings Green Line Default NA No No No No No NA 

Compass Green Line Default NA No No No No No NA 

Predicted 

track line 

Green Line Default NA No No No No No NA 

Geometric

graph 

Maps Yellow Line Seg E No No No No No NA 

(Continued on next page) 
8

Datablock 

Normal datablocks are green text. A controller can 

highlight a specific datablock by clicking it to temporarily change the text color to white. The alert messages 

about potential collisions are similar to those used on 

the ACD. Other than the red text of “CA” and “LA,” 

the alert messages of STARS also include other types of 

alert in blinking red. Like in ACDs, the red alert text 

alone is not salient enough to draw attention. However, 

the blinking signal is an effective visual attribute to gain 

attention. The red text also has low text readability. 

Aircraft symbol 

An aircraft symbol may consist of a search target 

symbol, or a beacon target symbol, or both. A search 

target symbol is green and a beacon target symbol is 

bright yellow. In addition, white is used to identify the 

symbol of an aircraft that is at the current scan position. 

Thus, the purpose of bright yellow, green, and white is 

to identify different types of symbols. The drawback is 

that each color had multiple uses in STARS. 

Weather

Weather information is presented on STARS with 

filled background areas that are overlaid with datablocks 

and aircraft symbols. Six levels of weather precipitation 

are displayed independently or simultaneously, based on 

weather selection. Combinations of overlaying stipple 

and colors are used to discriminate weather intensity 

levels. Controllers can determine each weather level in 

isolation based on the coding used. The coding scheme 

for weather levels is as follows: 

Weather Level 1 – dark gray-blue

Weather Level 2 – dark gray-blue, low density gray 

overlay stipple

Weather Level 3 – dark gray-blue, high density gray 

overlay stipple

Weather Level 4 – dark mustard 

Weather Level 5 – dark mustard, low density gray 

overlay stipple

Weather Level 6 – dark mustard, high density gray 

overlay stipple

Weather information is shown with these two low 

luminance colors to allow controllers to see aircraft datablocks, list data, aircraft symbols, and map data through 

the weather data. However, the readability of red alert 

messages in datablocks is below the error-free reading 

threshold when overlaid on dark gray-blue or dark mustard filled areas. Dark gray-blue for weather levels 1,2,3 

is not effective in identification because the chromaticity 

difference between dark gray-blue and dark blue (the 

background color) is less than the threshold. Another 

drawback is that the use of mustard for Levels 4,5, and 

6 may interfere with controllers’ experience of color use. 

Table 2: Color Documentation and Analysis for Standard Terminal Automation Replacement System 

(continued) 

Beacon Bright

yellow 

Shape Iden E No No No Y No NA 

Search target Green Shape Iden NA No No No Y No NA 

Current scans White Shape Iden E No No No Y No NA 

Aircraft

symbol 

History 

trail

Green Shape Seg E No No No No No NA 

Level 

1,2,3

Dark gray 

blue 

Filled

area

Iden NE No No No No No Y 

Level 

4,5,6

Dark

mustard

Filled

area

Iden E No No No No Y Y 

Weather 

stipple Gray Texture Seg E No No No No No NA 

Default colors Green for traffic situation area and white for toolbar area 

Sets of color-coding (Dark gray-blue, Dark mustard) for weather levels 

(Bright yellow, White, Green) for aircraft symbols 

(Yellow, White, Green) for coordination list 

(Red, green, white) for datablocks 

(Red, black) for system status alerts 

(Blue-gray, Selected blue-gray) for weather buttons on the menu bar 

Number of colors 15 

Number of color usages 31 
9

While Levels 4,5,6 represent heavy or severe weather, 

dark colors like mustard typically iminates non-critical 

information, so mustard may not alert controllers. 

Geographic restriction area 

A restriction area is indicated with a beige-filled circle 

or polygon. The text displayed within the circle or polygon 

is green. Controllers tend to rely on the shape rather than 

the color to identify geographic restriction areas. Because 

the shapes are distinctive from other materials on the 

display and can be reliably named (circle or polygon), 

they can be as effective as color for identification tasks. 

Thus, the purpose of the color was classified as segmentation, as the color is used to segment a restricted area 

from its surroundings. The readability of the green text 

on a beige background is below the threshold contrast 

for error-free reading.

Display-wide information

The display-wide information about color use in 

STARS is shown in the bottom portion of Table 2. The 

default colors are green for the traffic situations and white 

for the information in menu bars. Five sets of colors are 

used for identification. Notice that many colors are associated with multiple meanings. A total of 15 colors are 

used in STARS, while the total number of color uses is 

31. Many colors used in STARS have chromaticity values 

that are too close to be distinctively and reliably named. 

For instance, users would have difficulty in distinctively 

naming several colors “gray-blue,” “blue-gray,” “slateblue.” Therefore, while those colors can be used for the 

purpose of segmentation, they should not be used to 

identify categories of information.

Display System Replacement (DSR)

DSR is currently the primary display in most en route 

facilities. Like other primary displays, DSR has menu bars 

along the display and a traffic situation area on the central 

portion. The background color of a DSR display can be 

changed by controllers from dark blue to black. Datablocks and aircraft symbols are green. Alerted datablocks 

are indicated with blinking text. Only three components 

of a DSR display use color-coding: the weather display, 

fly-out window, and graphic tool. Below we describe the 

color analysis for these components. The summarized 

results of this analysis are presented in Table 3. 

Weather and Radar Processor (WARP) display

WARP presents specialized aviation weather products 

to support en route air traffic control operations. WARP 

provides Next Generation Doppler Weather Radar 

(NEXRAD) data for DSR with five weather levels: Level 

2 for moderate weather; Levels 3,4 for heavy weather, 

and Levels 5,6 for severe weather. Weather levels are 

represented by two colors and one color pattern: Level 2 

is purple, Levels 3,4 are turquoise and black checkboard; 

Table 3: Color Documentation and Analysis for Display System Replacement (DSR) 

Component Color Usage Purpose Eff Drawback factors 

Dis Unc Int Mul Exp Read 

Background Dark blue Filled 

whole 

screen

NA NA NA NA NA NA No NA 

Purple Filled area Iden E No No No No No Y 

TurquoiseblackFilled

checkboard 

Iden D No Y No No No Y 

Iden D 

Weather 

(WARP)

Turquoise Filled area 

Att E 

No Y No No Y Y 

Fly-out 

window 

Brown Text box Seg E No No No No No Y 

Red Filled area, 

text 

Iden E No No No No Y Y 

Yellow Filled area, 

text 

Iden E No No No No No No 

Green Filled area, 

text 

Iden NE No No No No Y No 

Graphic tool 

White Filled area, 

text 

Iden E No No No No No No 

Default color Green 

Sets of colorcoding (Red, Green, Yellow, White) for graphic tool 

(Purple, Turquoise) for weather 

Number of 

colors

8

Number of 

color usages 

9
10

and Levels 5,6 are turquoise. The color scheme for WARP 

has several drawbacks: 

1. Coding uncertainty in the use of turquoise. A user has 

to use the pattern cue to identify Level 3,4 weather 

from Level 5,6 weather. 

2. Low readability. The text of green datablocks has a 

low readability when overlaying with filled weather 

areas. 

3. Experience interference. The presence of Level 5,6 

weather is a critical event that requires controllers’ 

attention or alert. However, it was represented by 

turquoise, a color that usually would not trigger an 

alert. 

Fly-out window 

By clicking a datablock, a fly-out window appears 

next to the datablock. The window displays a column of 

altitude numbers for controllers to change the altitude 

of the aircraft in the flight plan (but does not cause the 

pilot to change altitude). The background of the window is white and the altitude text is black. The current 

altitude of the aircraft is highlighted with a brown text 

box. The luminance contrast of the black text on the 

brown background is below the threshold for error-free 

reading. However, controllers do not really need to read 

the current altitude. They tend to use the brown color as 

a reference mark: Moving up from the mark increases the 

altitude and moving down decreases the altitude. 

Graphic tool

The graphic tool allows controllers to pick up one of 

four colors to draw filled areas for specific flying regions. 

The route and distance from a given flight to a specified 

region is subsequently displayed with the same color. Thus, 

the colors are used for identification. The four colors are 

red, yellow, green, and white. Among them, green is not 

effective for identification because the default text color 

of the display is green. One drawback of the color use is 

experience interference, that is, red should be reserved only 

for critical information. Using red to label non-critical 

information is inconsistent with controllers’ experience 

of color use. In addition, the readability of the red text 

on the dark background is below the threshold for errorfree reading. Another drawback is that the use of green 

for identification is inconsistent with the convention of 

color use, as green is typically used as a default color and 

should not be assigned to specific meanings.

Display-wide information

The display-wide information about color use in DSRs 

is presented in the bottom portion of Table 3. The default color is green. Only seven colors are used in DSRs. 

The total number of color uses is eight. Only two sets 

of colors are used for identification: (red, green, yellow, 

and white) for the graphic tool and (purple, turquoise) 

for weather. 

Comparisons of Color Use in ATC Displays

Effectiveness and drawbacks

To compare the effect of color across displays, we 

calculated the number of situations in which color use is 

not effective for a given task purpose, or the effectiveness 

depends on other attributes besides color. That is, we 

counted the number of times “NE” and “D” appeared 

in the “Eff” column in each of the summary tables. We 

also calculated the number of drawback factors for each 

display, that is, the number of times “Y” occurred in the 

six right-most columns in each table. These two numbers 

together can reflect the overall effectiveness of color use 

in a display. Figure 1 shows the results. The upper and 

lower panels are for the effectiveness and drawbacks, respectively. From left to right along the horizontal axis are 

the three displays: ACD, STARS, and DSR. The vertical 

axis of the upper panel represents the number of situations 

where color use is either not effective or the effectiveness 

depends on other visual attributes (i.e., the number of 

“NE” and “D”). The vertical axis of the lower panel 

represents the number of situations where color use has 

the potential to negatively affect ATC task performance 

(i.e., the number of “Y” in drawback factors). Figure 1 

indicates that DSR has the lowest number of color use 

problems. In addition, while both ACD and STARS are 

the primary displays for terminal facilities, STARS has 

more problems in color use than ACD. 

0

5

10

15

20

No. of ineffective color use

0

5

10

15

20

No. of drawbacks

ACD STARS DSR

Figure 1: Effectiveness and drawbacks of color use in 

three primary ATC displays. The upper and lower 

panels are for effectiveness and drawbacks, 

respectively. The three displays are listed along the 

horizontal axis, with ACD, STARS, and DSR from left 

to right.
11

Notice that the two variables shown in Figure 1 are 

rough estimates of the effects of color in displays. Since 

the effectiveness and drawback factors are assessed on 

a simple yes / no scale, the results cannot accurately 

reflect the effects of a color use on task performance. In 

other words, two color uses that have “Yes” in the same 

drawback factor category may not affect controllers’ task 

performance to an equivalent degree. We will discuss this 

in detail later. 

Color complexity

Three indices were used to measure color complexity: 

the number of colors, the number of color uses, and the 

number of sets of color-coding. For any given task purpose, the effectiveness of color decreases with the increase 

of these indices (Xing, 2006a). Specifically, visual studies 

have demonstrated that the number of colors in a display 

should be fewer than 6~7. Beyond that, color has no 

advantage compared with achromatic attributes (Carter, 

1982). Also, Yuditsky et al. (2002) showed that color had 

no advantage when three sets of color-coding were used 

simultaneously to encode different parts of datablocks. 

Finally, the number of color uses provides a rough index 

of the mental workload imposed by colors. 

Figure 2 shows the three indices for each of the three 

displays (ACD, STARS, and DSR) and the corresponding 

upper-limits beyond which the effectiveness of color begins 

to decrease, if not completely diminish. In each panel, the 

vertical axis represents the overall index. The three displays 

are listed along the horizontal axis; from left to right are 

ACD, STARS, and DSR. The dashed horizontal line in 

the top and bottom panels each represents a saturation 

number beyond which the effectiveness of color begins 

to decrease. The upper-limit for the number of colors is 

six and the upper-limit for the number of color-coding 

sets is three, inferred from the literature cited previously. 

No data about the saturation number of color usages is 

available. Figure 2 shows that DSR is the only display 

that uses colors below the saturation lines. The other 

two displays use color beyond the one or both saturation 

lines, suggesting that the effect of color is not optimal 

for ACD and STARS. 

DISCUSSION AND CONCLUSIONS

This study analyzed color use for three primary ATC 

displays. It represents the first attempt to evaluate the 

efficiency of ATC technologies by using the same format 

of analysis across multiple displays. Some manufacturers 

provide information about color usage in their display 

interface specifications. However, such documents are 

not always available to other designers and FAA human 

factors practitioners. Also, the descriptions about color 

usage are often incomplete and not systematic. Moreover, 

manufacturers’ documentation does not provide information about the effectiveness and drawbacks of color 

use. Therefore, the information provided by this report 

is expected to benefit the design and evaluation of new 

ATC technologies.

0

10

20

30

No. of colors used

0

10

20

30

No. of color usage

0

2

4

6

8

No. of color-coding sets

ACD STARS DSR

Figure 2: Color complexity in the three primary ATC 

displays. The top, middle, and bottom panels correspond to 

the numbers of colors, color usages, and sets of colorcoding, respectively. 
12

Operational Effects of Drawbacks of Color Use in 

ATC Displays

A shortcoming of this study is that we only provided 

information about drawbacks of color use with a simple 

yes/no scale. Visual and cognitive researchers have studied 

the possible consequences of the drawback factors (Xing, 

2006a). However, most of those results were obtained 

through simplified lab experiments and may not be 

directly applicable to ATC operations. Therefore, even 

when a drawback factor for a color usage is identified, 

it may or may not produce a negative effect in real ATC 

operations. For example, in the DSR fly-out window, it 

is difficult to read the black text of the current altitude 

on the brown background. Thus, the factor of text readability was identified as “Y” for that color usage in Table 

3. However, controllers do not need to read the current 

altitude from the fly-out window. They only use the 

brown color as a reference mark to choose a new altitude. 

Hence, for those factors with a “Y” in Tables 1-6, the 

operational consequences can vary from case to case. 

The factor may distract controllers in some ways, such as 

increasing mental workload moderately, but the overall 

negative impact is negligible. Alternatively, the factor may 

potentially contribute to operational errors. Therefore, 

a future study should analyze operational drawbacks of 

the color use identified in this report.

Limitations of the Analysis

The analysis we performed in this study was for ideal 

viewing conditions, assuming that controllers have normal 

color vision and that computer monitors render colors 

as described in manufacturers’ manuals. However, ATC 

operations are not always performed under those ideal 

conditions. The current FAA’s color vision standard allows 

personnel with a certain degree of color vision deficiencies to enter into the controller workforce. While the 

issue of color vision deficiencies was beyond the scope of 

this report, developers of ATC technologies need to be 

aware of the potential effects on controllers with a color 

vision deficiency. 

On the equipment side, several factors may affect the 

displayed colors: 

1. Controllers can adjust the brightness of their computer 

screens. When the brightness is reduced, some low-luminance colors (such as those used for weather on DSR 

and STARS) may become invisible to controllers. 

2. The displays used in air traffic control towers are often 

viewed under strong ambient light. In those situations, 

the colors may appear “washed out” so the color-­coding 

becomes ineffective. 

3. ATC displays are often viewed from off-axis view angles 

but different view angles cause significant variations 

in displayed colors on flat-panel displays. Therefore, 

when viewed from off-axis angles, text and graphics 

may have a loss of luminance contrast and undesirable 

variations in color. 

Because of the presence of color deficient controllers 

and those undesirable, but inevitable, viewing conditions, 

it is always important that the use of color in ATC displays should be accompanied by achromatic redundant 

cues. The use and effectiveness of redundant cues in 

ATC displays have been separately addressed in another 

report (Xing, 2006c). 

CONCLUSIONS

This report has achieved several goals. First, it provided a systematic documentation of color use in three 

ATC displays. Manufacturers and interface designers 

in ATC facilities can use this document as a reference 

to improve compatibility and consistency of their new 

ATC products to existing operational displays. Also, 

such a document can be used for other aviation research, 

such as the development of color vision standards for air 

traffic control specialist applicants. Second, it provides 

analytic results about the effectiveness and drawbacks 

of color use in ATC displays. Such information is useful for the evaluation of proposed automation systems 

at acquisition. Third, the results can help display users 

(training supervisors and controllers at ATC facilities) 

to become aware of potential negative consequences of 

color use so that they can try to avoid situations where 

a color use can contribute to operational deviations and 

errors. Finally, this study provided a general method for 

human factors practices in the design and evaluation of 

human-computer interaction systems. 

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A1

APPENDIX A 

Table A-1. A Checklist for the Effectiveness of the Use of Color in ATC Displays 

Task purpose Color and 

visual factors 

Conditions for color-use being effective Yes 

/ No 

Luminance The luminance of the color-coded target is greater 

than or equal to that of distractors (i.e., other materials 

displayed in the visual field). 

Luminance and 

chromaticity 

The luminance difference between the color-coded 

target and distractors is greater than 20cd/cm2

regardless the chromaticity difference. Alternatively, 

the chromaticity difference between the color-coded 

target and distractors should be greater than 0.24 in 

CIE chromaticity coordinates. 

Attention

Number of 

distractor 

colors 

The number of distractor colors should be less than 

3~4 (The number of colors of the distractors with a 

size greater than or equivalent to that of the target 

should be minimized). 

Color naming The colors used for identification can be named 

uniquely and consistently. 

Chromaticity The chromaticity differences between the colors are 

greater than 0.036. 

Luminance The luminance differences between colors are less 

than 20cd/cm2

.

Identification 

Number of set 

colors 

The number of colors is less than 7. 

Luminance or 

Chromaticity 

For regional object segmentation, the chromaticity 

difference between the object and its surrounds is 

greater than 0.004. Alternatively, the luminance ratio, 

defined as the absolute luminance difference between 

the object and surrounds divided by the luminance of 

the object, is greater than ~5%. 

For pattern segmentation, the color difference 

between the pattern and its surrounds is greater than 

0.02. Alternatively, the luminance ratio is greater than 

15~20%.

Segmentation 

No. of object 

colors 

The number of colors of the object to be segmented is 

less than 2 unless the object is composed of a 

regularly patterned texture of different colors. 

B1

APPENDIX B 

Table B-1. A Checklist of Drawbacks of Color Use in ATC Displays 

Color and visual 

factor 

Conditions for inducing 

drawbacks 

Potential consequences 

induced by the factor 

Yes 

/ No 

Distraction Multiple colored targets for 

attention are onset 

simultaneously within the view 

field.

Only one of the targets captures 

attention; others could be 

ignored.

Coding uncertainty Messages (text or symbols) 

identified by colors do not have a 

unique meaning; thus, color 

cannot serve as the selection 

criteria.

Slower and less accurate in 

identification compared to using 

text or symbols alone. 

Loss of integration Color-segmented messages 

need to be considered together 

simultaneously for task 

performance. 

Less chance to associate pieces 

of information that are color 

segmented. 

1) More than 3 sets of colorcoding in a display. Increasing chances of missing 

information; users tend to ignore 

color-coding. 

Multiple color 

schemes 

2) One color is used for multiple 

purposes, or multiple colors are 

used for the same purpose. 

Increasing cognitive workload; 

slower in interpreting 

information; increasing chances 

of misinterpreting information. 

Experience 

interference 

Color use differs from controllers’ 

experience (such as red for noncritical information). 

Increasing chances of 

misinterpreting information. 

Text readability The luminance contrast between 

the text and background colors is 

less than the threshold contrast 

(20~30%) for error-free reading. 

Reducing reading speed; 

increasing reading errors. 

C1

APPENDIX C 

Transformations Between Digital Values of a Displayed Color and CIE Chromaticity 

Coordinates

Colors in a computer display can be described by the tri-stimulus color system. This system 

specifies a color with three photometric quantities: R, G, and B. Given (r, g, b) as the 8-bit digital 

values for each of the red, green, and blue channels of a monitor, the relationship between RGB 

values and digital values is determined by the following equations:

R=(r/255)gamma

G=(g/255)gamma 

B=(b/255)gamma 

Where Gamma is a parameter of a monitor that specifies the nonlinear relationship between 

the rgb values and the rendered luminance. The Gamma value for CRT displays generally varies 

in the range of 1.8~2.5, with a typical default value of 2.2. 

And,

X=40.9568*R + 35.5041*G + 17.9167*B; 

Y=21.3389*R + 70.6743*G + 7.98680*B; 

Z=1.86297*R + 11.4620*G + 91.2367*B.

Note that the parameters in these transformations vary from monitor to monitor. We will use 

these default values for the computation in this report. 

Then,

x=X/(X+Y+Z); 

y=Y/(X+Y+Z); 

L=Y