Color Analysis in 

Air Traffic Control 

Displays, Part II. 

Auxiliary Displays

Jing Xing

Civil Aerospace Medical Institute

Federal Aviation Administration

Oklahoma City, OK 73125

March 2007

Final Report

DOT/FAA/AM-07/5

Office of Aerospace Medicine

Washington, DC 20591
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1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. 

DOT/FAA/AM-07/5 

4. Title and Subtitle 5. Report Date 

Color Analysis in Air Traffic Control Displays, Part II. Auxiliary Displays March 2007 

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 

This report presents the second part of our analysis of color use in Air Traffic Control displays. Part I of the 

study focused on operational displays, while this investigation focuses on auxiliary information displays with 

which controllers acquire additional information to make decisions. We chose three frequently used decisionsupport displays for the analysis. Those are: User Request Evaluation Tool (URET), Traffic Management 

Advisor (TMA), and Integrated Terminal Weather System (ITWS). For each display, we documented the 

background and default colors, color-coding, color usage, associated purposes of color use, and color complexity. 

With this systematic documentation, we were able to assess compatibility across displays. Using the color 

checklists we developed earlier, we also analyzed the effectiveness and shortcomings of color use in these displays. 

The results revealed a number of instances where the use of color might not be effective for its given purpose and 

where a color could have potential negative effects on task performance. The results of this study can benefit 

design prototypes and acquisition evaluation for new Air Traffic Control technologies. 

 

17. Key Words 18. Distribution Statement 

 

 

ATC Displays, Color, Evaluation, Human Factors, 

Redundant Cue

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 

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Unclassified Unclassified 19 

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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. Dr. Pam Della Rocco proposed the method of documenting 

color use in ATC displays. This project could not have been done without their help. 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 all the FAA reviewers and editors whose efforts greatly improved 

this report.

Contents

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

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

RESULTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

User Request Evaluation Tool (URET) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Traffic Management Advisor (TMA). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Integrated Terminal Weather System (ITWS). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Effectiveness and drawbacks of color use in the three displays. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Color complexity in the three displays. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Color consistency across displays. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

DISCUSSION AND CONCLUSIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

REFERENCES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Color Analysis in Air Traffic Control Displays, 

Part II. Auxiliary Displays

INTRODUCTION

In our companion report “Color analysis in air traffic 

control displays, Part I. Radar displays” (Xing, 2006a), 

we documented and analyzed color in three operational 

displays: Automated Radar Terminal System Color Display (ACD), Standard Terminal Automation Replacement 

System (STARS), and Display System Replacement 

(DSR). While operational controllers primarily use radar 

displays to assist them in controlling traffic, they also 

frequently acquire information from auxiliary displays. 

For example, an en route controller needs to be aware of 

potential conflicts of aircraft in the near future and resolve 

them ahead of time. Instead of generating a complicated 

mental computation to figure out potential conflicts, 

the controller can use a User Request Evaluation Tool 

(URET) that displays the status of aircraft potential conflicts in different colors. Since such tools are intended to 

assist controllers’ work, it is critical that the tools present 

information in a consistent (or at least compatible) manner with the information presented in the radar displays 

(Cardosi, 2003). However, the compatibility between 

the ATC displays has not received sufficient attention 

from the developers of ATC technologies, partly because 

there is a lack of systematic documentation of display 

specifications. Developers often fail to identify the colors 

used in other ATC displays. Therefore, one purpose of 

this study was to introduce a method for developers to 

document the use of color to improve the compatibility 

of ATC technologies. 

Previously, we conducted a series of facility observations of color use in ATC displays (Xing & Schroeder, 

2006). We found that most decision-support tools used 

colors more extensively than the radar displays. In general, 

decision-support tools used a large number of colors that 

did not comply with the human factors guidelines for the 

use of color in visual displays (Cardosi & Hannon, 1999; 

HF-STD-001, 2003). As a result, some colors are not effective for the given tasks, providing limited support for 

decision-making. Even worse, some color uses have the 

potential to negatively affect controllers’ task performance. 

In addition, there appears to be discrepancies between what 

the developers wanted to convey by color-coding and what 

the controllers perceived. During our facility observations, 

we observed circumstances where controllers did not know 

or remember the meanings of colors in the decision-support 

displays. Therefore, another purpose of this study was to 

establish an example for developers to self-evaluate the use 

of color to improve the usefulness of their ATC tools. 

While there are only a few types of radar displays, 

there is considerable variation in decision-support tools 

across ATC facilities. Moreover, some auxiliary displays 

allow controllers to set up color schemes based on their 

own preference. Thus, this report was not intended to 

cover the majority of decision-support tools. Instead, 

we chose several representative tools currently used in 

en route and terminal facilities for color documentation 

and analysis. Those are:

•	 User Request Evaluation Tool (URET) — URET is 

a major support display implemented in the en route 

facilities with the removal of flight progress strips.

•	 Traffic Management Advisor (TMA) — TMA is another auxiliary display used in en route facilities.

•	 Integrated Terminal Weather System (ITWS) — ITWS 

is a major weather display in terminal facilities. Since 

ITWS integrates many weather products, some parts 

of its color schemes are also used in other weather 

products such as Weather System Processor and Terminal Doppler Weather Radar (TDWR).

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

analyze the benefits and drawbacks of color use in several representative auxiliary displays; and 2) to provide a 

systematic documentation of color use in those displays. 

For each of the three displays, 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

The methods are essentially the same as those used in 

the companion paper (Xing, 2006a). In brief, we applied 

the two color-use checklists developed by Xing (2006b) to 

assess the colors used in the three displays. The companion 

paper provided the two checklists in its Appendices. For 

each display, we first analyzed the use of color in individual functional components (such as datablock, menu, 

list, and maps). The analysis includes the task purpose 

associated with a color, the effectiveness of the color for 

the task purpose, and six potential drawback factors that 

may negatively affect task performance. 
Previous work classified three categories of purposes associated with color use in ATC displays: 1) draw attention 

to critical events; 2) identify categories of information; 

and 3) segment complex scenes. We referred to those 

purposes as attention, identification, and segmentation

(Xing & Schroeder, 2006). 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. 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. 

The six potential drawback factors can be briefly described as the follows: 1) Distraction: Multiple colored 

objects for attention are simultaneously presented within 

the visual field. 2) Coding uncertainty: Messages (text 

or symbols) identified by colors do not have a unique 

meaning in identification tasks. 3) Loss of integration: 

Messages in different colors need to be considered together simultaneously for successful task performance. 

4) Multiple color schemes: One color is used for multiple 

purposes or multiple colors represent the same meaning. 

5) Experience interference: Color use is against controllers’ 

experience, such as red for non-critical information, or 

dark colors for critical information. 6) Text readability: 

The luminance contrast between text and background 

colors is less than the threshold contrast (typically taken 

as 20%) for error-free reading. These six factors were 

examined for each color use and the results were classified as either “Y” or “No.” “Y” means that the drawback 

factor exists; thus, the color usage has the potential to 

negatively affect task performance. “No” means that the 

factor does not exist for the given color usage. 

We then document the general information including 

background colors, default colors, and color complexity. 

The complexity is composed of three metrics: the total 

number of colors in the display (excluding the background 

color), the total number of colors used for identification, 

and the number of sets of color coding, where each set of 

colors is used to identify different aspects of the data.

RESULTS

This section includes two parts: The first part describes 

the color documentation and analysis for each ATC display. 

For each display, we briefly described color usage for each 

functional component, pointed out the situations where 

color use was not effective or had potential drawbacks, and 

analyzed color complexity. The results for each display are 

presented in a summary table. The second part provides 

a comparison of color use across displays. 

User Request Evaluation Tool (URET) 

URET is a tool that supports decision-making for en 

route controllers. A URET display is organized into seven 

windows. The main page has a black background and 

contains only a toolbar of buttons for window selection. 

The text of selection buttons is white. Since controllers 

frequently use only three of the seven windows (Aircraft 

List, Graphic Display, and Plans Display), we analyzed 

color use for these three windows. 

Aircraft list

The aircraft list window has a horizontal title bar 

across the window on the upper portion and several lists 

occupying the majority of the window. The title bar text 

is black, and the background is filled with a bright cyan 

color. It is so salient that it can distract a user’s attention 

from other materials in the window. However, this bar 

contains little information and does not require the 

controller’s attention. 

The aircraft list displays several types of text information. The elements in the list (from left to right) are flight 

status, flight ID, altitude, and routes. The background 

color of the list is black. The default text color is white. 

Flight status is indicated with text boxes in three columns. 

The frames of the boxes are white lines, and the texts are 

color-coded with red / muted red, yellow / muted yellow, 

cyan, and brown. Muted red and muted yellow have the 

same chromaticity as red and yellow, respectively. However, 

the luminance is lower for the muted colors. A flight in 

normal status is shown as a white box frame without any 

text in it. When a loss of separation is predicted, the box 

frame in the left-most column turns red or muted red, 

and a letter “R” is displayed in the box. The text matches 

the color of the box frame. Red represents predicted loss 

of separation within 5 miles. Therefore, red represents 

an alert that requires the controllers’ attention. Muted 

red represents that the aircraft is not on its original flight 

plan and will develop a loss of separation if the controller 

takes some expected action. In the second column, yellow 

represents potential conflicts between aircraft predicted to 

come within 5-12 miles of each other, while muted yellow 

represents that a loss of separation within 5-12 miles will 

develop if the controller takes some expected action. The 

cyan color in the third column of boxes indicates aircraft 

that are predicted to conflict with a restricted airspace. 

There can also be numbers in the boxes to indicate the 

number of aircraft involved. The brown color appears in 

all three columns for a flight that has no tracking data; 

thus, auto-prediction is not available. The brown boxes 

are accompanied with a symbol “X” in them. Each of 

these colors has a different meaning, and controllers have 
to associate the colors with their meanings. Therefore, we 

classified the purposes of these colors as identification.

The text in the Flight ID list is white for normal flights, 

brown for flights without tracking data, and orange for 

overdue flights. The Flight altitude list uses white text 

for filed altitude and yellow text for changed altitude. 

Route information is displayed with texts in two colors for 

segmentation. However, because controllers are required 

to read the text to acquire information, the meaning of 

the colors is not significant to them.

Red and muted red are used for attention and identification. The low luminance of the red letter “R” and 

the frame of the text box are not salient enough to draw 

attention. As for identification, while red can effectively 

identify the aircraft status from those in white and brown, 

it cannot effectively identify the status from the ones in 

muted red. Thus, a user may encounter difficulties in 

differentiating aircraft status coded in red and muted red 

just based on the luminance difference between them. The 

same is true for yellow and muted yellow. In addition, the 

text readability for red, muted red, and muted yellow is 

low. Yellow is used for potential conflict in Flight Status 

and for changed altitude in the Altitude column; thus, 

the color has multiple meanings. 

Graphic display

The graphic display illustrates datablocks and routes, 

special airport codes, and restricted airspace for aircraft 

on a 2-dimensional map. The color scheme of datablocks 

and routes is consistent with that used in the aircraft 

list. White datablocks and routes mean normal. Red, 

muted red, yellow, muted yellow, and cyan have the same 

meanings as those in the aircraft list. The drawbacks of 

color use are the same as those in aircraft list, except 

that red might be effective for attention in this window, 

depending on the line lengths of routes. We classified the 

effectiveness as “D.” 

Plans display

The plans display shows text information about the 

flight plan evaluation. Green text represents no conflict 

while red text is used to show a conflict. Both colors are 

for identification. The colors are effective for this purpose. 

A drawback is that the readability of the red text is low.

General information

A good color strategy in URET is that color schemes 

across individual functional windows are consistent. The 

same color is used in all the windows for the same task 

purpose and with the same meanings. For instance, blue 

is used as the background color of menu bars in all the 

three functional windows and the main page. Thus, the use 

of blue is counted as one although it appears four times. 

The background color is always black. The background 

of menu bars in all the windows is blue. The default 

text color is white for black and blue backgrounds and 

black on the cyan background of title bars. Nine colors 

are used in URET. The number of color uses is 16. Six 

sets of color-coding are used for identification. Among 

the colors, cyan and yellow encode multiple types of 

information. 

The results of color analysis in URET are summarized 

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. We used the 

following symbols to represent the six factors: “Dis” for 

distraction, “Unc” for coding uncertainty, “Int” for loss of 

integration, “Mul” for multiple color schemes, “Exp” for 

experience interference, and “Read” for text readability. In 

the “task purpose” column, we used “Att” for Attention, 

“Iden” for Identification, and “Seg” for Segmentation. 

The overall color use information in URET, (listed in the 

bottom portion of Table 1) includes background colors, 

default colors, and the three metrics of color complexity 

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

of color usage). 

Traffic Management Advisor (TMA)

TMA is a support display used in both en route 

and terminal facilities. The display provides a number 

of graphical components to improve users’ situational 

awareness. The graphical components deployed at ATC 

facilities include timeline and load graphs. Like URET, 

the main page of TMA only contains a menu bar. Each 

component can be displayed in a window by clicking the 

selection buttons on the bar. Table 2 shows the summary 

results of color analysis for TMA.

Timeline

The timeline displays text about time axis, aircraft 

tag, tracking symbol, and delay time along a vertical axis 

indicating time. The background color of the Timeline 

window is black. The default color is white for the time 

axis. An aircraft tag may appear in one of three colors: 

green for normal arrival, yellow for unfrozen scheduled 

time of arrivals (STAs), and turquoise for frozen STAs. 

A frozen STA means that the aircraft is close enough to 

the meter fix that the time of arrival will not be changed 

except in response to extraordinary events. An unfrozen 

STA means that TMA schedulers can change the displayed 

STA. A tracking symbol composed of a small arrow and 

a short line connects every aircraft tag to the time axis. 

Each symbol is in the same color as the aircraft tag it 

connects unless TMA has not received any radar tracks 
Table 1. URET color documentation and analysis 

Window Component Color Usage Purpose Eff Drawback factors 

Dis Unc Int Mul Exp Read 

Background Black Filled 

screen

NA NA NA NA NA NA No NA 

Menu bar 

background 

Blue Filled 

bar

Seg E No No No No No NA 

Main

window 

Menu bar text White Text Default NA No No No No No No 

Background Black Filled 

screen

NA NA NA NA NA NA No NA 

Menu bar 

background 

Blue Field bar Seg E No No No No No NA 

Menu bar text White Text Default NA No No No No No No 

Title bar 

background 

Cyan Filled bar Seg E Y No No No No No 

Title bar text Black Ttext Default NA No No No No No No 

Frames of list White Lines Default NA No No No No No NA 

Flight status White Text Default NA No No No No No No 

Red Text Att NE 

Iden NE 

No No No No No Y 

Muted 

red

Text Iden NE No Y No No No Y 

Yellow Text Iden NE No No No Y No No 

Muted 

yellow 

Text Iden NE No Y No No No Y 

Cyan Text Iden E No No No Y No No 

Brown Text Iden E No No No No No NA 

Flight ID White Text Default NA No No No No No No 

Orange Text Iden E No No No No No No 

Brown Text Iden E No No No No No No 

Altitude White Text Default NA No No No No No No 

Yellow Text Iden E No No No Y No No 

Route White Text Default NA No No No No No No 

Cyan Text Seg E No No No Y No No 

Aircraft

list

Brown Text Seg E No No No No No No 

Background Black NA NA NA NA NA No NA 

Title bar 

background 

Cyan Filled bar Seg E Y No No No No NA 

Title bar text Black Text Default NA No No No No No No 

White Text, line Default NA No No No No No No 

red Text, line Att D 

Iden NE 

No No No No No No 

Muted

red

Text, line Iden NE No No No No No Y 

Yellow Text, line Iden NE No No No No No No 

Datablock and 

routes

Muted

yellow 

Text, line Iden NE No No No No No No 

Airport code in 

datablock 

Cyan Box 

frame

Iden E No No Y Y No No 

Graphic

display 

Spacial zone Cyan Line 

frame

Iden E No No No Y No No 

(Continued next page) 
Table 1. URET color documentation and analysis (continued) 

Background Black NA NA NA NA NA NA No NA 

Title bar 

background 

Cyan Filled bar Seg E Y No No Y No No 

Title bar text black Text Default NA No No No No No No 

Red Text Iden E No No No No No Y 

Plan

display 

Plan evaluation 

Green Text Iden E No No No No No No 

Default color White and occasionally black if the background is a bright color 

Sets of color-coding 

(Red, Yellow, Brown, Cyan) for flight status 

(Brown, Orange) for flight ID 

(Cyan, Brown) for route 

(Brown, Yellow) for altitude 

(Cyan) for special flight zone 

(Red, Green) for plan evaluation 

Number of colors 9 

Number of color usage 16 

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 applicable D ̛ The effectiveness of color 

depends on other factors 

Y ̛ yes 
Table 2: TMA color documentation and analysis 

Window Component Color Usage Purpose Eff Drawback factors 

Dis Unc Int Mul Exp Rea

d

Background Black Filled 

area

NA NA NA NA NA NA No NA 

Menu bar 

background 

Cyan Filled 

bar

Seg E No No No No No NA 

Main

window 

Menu bar text White Text Default NA No No No No No No 

Background Black Filled 

area

NA NA No No No No No NA 

Titlebar Cyan Filled strip Seg E No No No No No NA 

Title text White Text Default NA No No No No No No 

Time axis White Line, Text Default NA No No No No No No 

Green Text Iden E No No No Y Y No 

Yellow Text Iden E No No No Y No No 

Aircraft tag 

Turquoise Text Iden E No No No Y No No 

Tracking 

symbol 

Orange Lined 

symbol 

Iden E No No No Y No No 

Red Text Iden E No Y No Y Y Y 

Yellow Text Iden E No Y No Y No No 

Orange Text Iden E No Y No Y No No 

Delay time 

Green Text Iden E No Y No Y No No 

Timeline 

Rush alert Red Heavy 

brackets

Att E No No No No No No 

Background Black Filled area NA NA No No No No No No 

Axes White Line, 

Text 

Default NA No No No No No No 

Yellow Curve Iden E No No No Y No No 

Green Curve Iden E No No No Y No No 

Curves

Turquoise Curve Iden E No No No Y No No 

Load 

graph 

Capacity 

indication 

Red Line Iden E No No No Y Y No 

Default color White for graphics and green for text of normal status 

Sets of color-coding 

(Green, Yellow, Turquoise) for aircraft tag 

(Orange) for aircraft without tracking information 

(Red, Yellow, Orange, Green) for delay time 

(Yellow, Green, Turquoise) for curves of load graph 

Number of colors 7 

Number of color usage 17 
for that aircraft. In that case, TMA computes time of 

arrival using the filed flight plan of the aircraft, and the 

symbol is displayed in orange.

The delay time for every aircraft is displayed as the 

number of minutes along the time axis. The four colors 

indicate length of delay: green for 0-5 min, yellow for 

delays of 5-10 min, orange for delays of 11–15 min, and 

red for delays longer than 15 min. Thus, the four colors 

are used to identify lengths of delay, yet red is also used 

to capture users’ attention. A pair of red heavy brackets 

on the time axis indicates a rush-time alert. 

Timeline uses three sets of color-coding to identify 

different types of information: (green, yellow, and turquoise) for aircraft tag, (orange) for tracking symbol, and 

(red, orange, yellow, green) for delay time. An apparent 

drawback is that green, yellow, and orange are all assigned 

to more than one meaning. Also, red is used for both rush 

time alert and the longest period of delay time.

The color-coding of delay time has several drawbacks. 

One of these is coding uncertainty. While colors represent 

four distinctive categories of delay time, users need to 

know the exact amount of delay time. Thus, users have 

to make an effort to ignore the meaning of the color and 

acquire the information by reading the text. In addition, 

it is questionable whether red should be used to identify 

the category of delay time longer than 15 min. Lengthy 

delays are not as critical as a warning or alert message, 

although long delay times are important for users to be 

aware of. The last drawback is the low text readability of 

red on a black background. 

Load graph

The load graph shows present and future traffic flows. 

The graph displays two curves along the horizontal time 

axis: Green indicates the expected traffic demand, and a 

yellow curve indicates the planned arrivals. In addition, 

a red horizontal line indicates the airport acceptance rate 

set in TMA. The use of red in this instance is against 

the convention that red should be reserved for alerts. 

Both green and yellow are already assigned to multiple 

meanings in the timeline. In real operations, users often 

overlay a small load graph window with the timeline 

window. Therefore, green and yellow would each represent three different types of information within the 

same view field. 

General information

The default color is white for axes on the timeline and 

load graph. There is no default color for text; even green 

is associated with specific meanings. Therefore, a user has 

to remember and comprehend color meanings for every 

displayed item other than the axes, and that imposes an 

additional mental workload on users. As for color complexity, seven colors are used. The total number of color 

uses is 17. Four sets of colors are used for identification, 

and nearly every color is used to identify multiple types 

of information.

Integrated Terminal Weather System (ITWS)

ITWS is an automated weather information system 

that is used at terminal facilities. ITWS integrates a 

number of products that detect and predict such various 

types of weather as windshear, microburst, gust fronts, 

and tornadoes. The system also displays precipitation, 

tracks speed and direction of storm cells, and predicts the 

movement of storms. The display components of ITWS 

include product status, alert panel, graphics product, 

and site situation display. On the upper portion of the 

display are alert panel and product status buttons; the 

lower portion displays the graphics product. The site 

situation display is in a click-to-open window that is 

often overlaid with the graphics product. The results of 

the color use analysis for these components are described 

next and summarized in Table 3. 

Product status 

The product status panel consists of text buttons that 

show the status of the weather products in the graphic 

product display. Each button contains black text, indicating the product represented in this button. For example, 

“Precip” represents precipitation and “MB” represents 

microburst. The background color of a button reflects 

the status of the associated weather product. If a product 

is unavailable, the button is red. If a product is available 

and activated, the button is green. If a product is available but deactivated, the button is white. If the product is 

available and is being filtered, the button is yellow. If the 

product is not supported, the button is gray. Therefore, 

red, green, yellow, white, and gray are used to identify the 

status of weather products. There is no redundant cue for 

the product status; the text and position of a button only 

indicate the type of the product but not the status. 

Several drawback factors exist in the product status 

color-coding set: 1) all four colors are used to represent 

other types of information in ITWS; 2) while not intended 

to draw attention, the white, yellow, and red buttons 

are so salient that they could distract a user’s attention 

from other displayed materials; and 3) the uses of white 

and red are against the conventions of color use; that is, 

white is typically for the default or normal status, and 

red should be reserved for information that needs immediate attention. 


Table 3: ITWS color documentation and analysis 

Drawback factors 

Component Color Usage Purpose 

Eff

Dis Unc Int Mul Exp Read 

Background Gray Filled 

screen

NA NA NA NA NA NA No NA 

Gray Filled 

area

Background Default NA NA NA NA NA No NA 

Green Filled 

box 

Iden E No No No Y No No 

White Filled 

box 

Background Iden E Y No No Y Y No 

of buttons 

Yellow Filled 

box 

Iden E Y No No Y No No 

Red Filled 

box 

Iden E Y No No Y Y No 

Product

status

Button text 

Black Text Default NA No No No No No No 

Gray Filled 

area

Default NA NA NA NA NA No NA 

Green Filled Iden NE 

area Att D 

No No No Y No No 

Yellow Filled Iden NE 

area Att D 

Y No No Y No No 

Purple Filled Iden NE 

area Att NE 

No No No No Y No 

Red Filled Iden NE 

area Att D 

Y Y No Y No No 

White Filled Iden NE 

area Att D 

Y No No Y No No 

Iden NE 

Background 

of buttons 

Black Filled 

area Att NE 

No Y No Y Y No 

Black Text Default NA No No No No No No 

Alert

buttons

Button text 

White Text Default No No No No No No 

Background Gray Filled 

window 

Default NA NA NA NA NA No NA 

Map Black Line Default NA NA NA NA NA No NA 

Light Green Filled area Iden NE No No No Y No NA 

Green Filled area Iden NE No No No Y Y NA 

Yellow Filled area Iden E No No No Y No NA 

Light orange Filled area Iden NE No No No Y No NA 

Orange Filled area Iden NE No No No No No NA 

Iden NE 

Precipitation 

Red Filled area 

Att D 

Y No No Y No NA 

Windshear Red Open Iden D 

circle Att NE 

Y No No Y No NA 

Microburst Red Filled Iden D 

circle Att NE 

Y No No Y No NA 

Gust front Purple Line Iden D 

Att NE 

Y No No No No NA 

Graphics

product 

(Continued next page) 
Table 3: ITWS color documentation and analysis (continued) 

Graphics Iden NE 

product 

Tornado Black Filled 

triangle Att NE 

No No No Y No NA 

Window 

background 

Slate blue Filled 

window 

 NA NA NA NA NA Y NA 

Title bar 

background 

Blue Filled bar Seg E No No No No No NA 

Title text White Text Default NA No No No No No No 

Menu bar Gray Filled bar Default NA No No No No No No 

Menu text Black Text Default NA No No No No No No 

Table 

background 

Gray Filled 

area

Default NA No No No No No No 

Table frame White Lines Default NA No No No No No No 

Table title Red Seg E No No No Y Y No 

Table text Black Default 

Red Filled Iden E 

box Att NE 

No No No Y No No 

Yellow Filled 

box 

Iden E No No No Y No No 

Blue Filled 

box 

Iden E No No No No No No 

Site

situation 

display 

Airport code 

Black Filled 

box 

Iden E No No No Y Y No 

Default color Black 

Sets of color coding 

(Green, White, Yellow, Red) for product status 

(Gray, Red) for airport indicator 

(Gray, White) for product automatic transition indicator 

(Green, Red) for TDWR status 

(Green, Yellow, Purple, Red, White, Black) for weather alerts 

(Light green, Green, Yellow, Light orange, Orange, Red) for precipitation 

(Red, Yellow, Blue, Black) for airport code 

Number of colors 9 

Number of color usages 24 
10

Alert panel

The alert panel, located in the upper-right portion 

of the ITWS display, consists of one or more rows of 

nine element boxes. Each row represents an airport. 

The elements (from left to right) are the airport indicator, product automatic transition indicator, status of 

TDWR, and six weather alert products. The default 

color of the airport indicator box is gray and red when a 

severe weather alert is detected. The product automatic 

transition indicator box is gray for manual transition 

and white for automatic transition. The TDWR status 

box is green if the product is available and red when it 

is not available. When hazardous weather is detected in 

a terminal area, the boxes of the six alert products light 

up. An alert box is gray when the product is not available or no alert is detected. When an alert is detected, 

the corresponding box lights up with a specific color. 

The colors are red for microburst, white for windshear, 

purple for gust front impacting within 20 min, yellow 

for lightning within 20 miles, and black for tornado 

and anomalous propagation. By lighting these boxes 

with colors, the display draws a user’s attention to the 

situations that may be potentially dangerous or may 

require a change in the runway configuration or airspace. 

Therefore, the colors are used mainly for attention. The 

colors also help users to identify types of weather, with 

location and text being the redundant cues. The default 

text color is black for most of the boxes and white for 

the purple and black boxes to enhance readability. An 

exception is that the text is red to draw attention to the 

white box when a windshear alert is detected. 

Seven colors are used in the alert panel. Each color 

identifies one or several types of information. However, 

the colors appear to have limited effectiveness. Visual 

experiments have demonstrated that the advantages of 

color in identification tasks disappeared when the number 

of colors reached 6~7 (Carter, 1982). The lighted colors 

are also used to draw attention. Among them, black and 

purple are not effective for attention because of their low 

luminance. Additionally, while red, white, and yellow are 

salient enough to draw attention out of the boxes in gray 

(the normal status), the effectiveness is dependent upon 

no other boxes being lit. A user cannot effectively attend 

to a salient target when more than two other targets are 

also salient in the field of view (Julesz, 1965). In addition, 

the red text for detected windshear is not salient enough 

to effectively draw attention because it is displayed in a 

white-filled text box. 

Color use in the alert panel has several drawbacks. First, 

there is uncertainty in the red and black categories. Red 

has multiple meanings in the panel; therefore, a user must 

use additional cues such as the text or button location to 

infer the meaning of red. The same is true for black, as it 

may mean either a tornado or an anomalous propagation. 

Second, most of the colors (green, red, white, yellow, and 

black) are used in other parts of ITWS for other purposes. 

Third, the use of black and purple for attention is against 

the conventions of color use.

Graphics product 

This product displays weather precipitation in filled 

areas. Intensity values of precipitation are based on National Weather Service intensity levels. Six colors (light 

green, green, yellow, light orange, orange, and red) 

represent level-1 to level-6 precipitation. The graphics 

product also displays severe weather including microbursts, windshear, gust fronts, and tornado alerts. Each 

of these weather types is indicated with a specific color 

and a shape (as the redundant cue) and is overlaid with 

areas of precipitation. Gust fronts are displayed as solid 

purple lines corresponding to the location of detected 

gust fronts, as well as dashed purple lines indicating 

the predicted position of the gust front in 10 and 20 

min. Detected windshears are presented as open red 

circles with the corresponding strength indicated inside 

the circle. Microbursts are presented as solid red circles 

with the strength indicated inside the circle. Detected 

tornatoes are presented as solid black triangles inside an 

open black circle. 

While six colors are used to identify precipitation 

levels, the chromaticity difference between light green 

and green is too small for users to reliably identify level 

1 from level 2 precipitation. When these two colors are 

used for identification together with many other colors, 

users tend to merge the two colors into one “green” 

category. The same is true for orange and light orange. 

Thus, these four colors, green, light green, orange, and 

light orange, cannot effectively identify the four assigned weather levels. Red represents the highest level of 

precipitation; thus, it is used for both identification and 

attention. Its effectiveness in attention depends on the 

size of the filled area. When the area is relatively large, 

it can potentially distract the perception of other severe 

weather alerts, and the detectability of those alerts is 

consequently reduced.

Three colors, red, purple, and black, are used for severe 

weather alerts that overlay filled precipitation areas. These 

colors are used for both attention and identification. 

As stated earlier, purple and black are not effective for 

attention. The effectiveness of red in attention depends 

on the size of the microburst or windshear circles. The 

effectiveness in identification depends on how many 

colors of precipitation exist in the view field. 
11

Site Situation Display

The Site Situation Display presents a table of weather 

situations for a number of terminal areas. Each row 

represents an airport. The background of the window is 

slate blue, and the background of the table is gray. The 

elements in the table (from left to right) are: airport code, 

mode, alert, and storm information. The title texts of 

elements are red. The text background of airport codes is 

color-coded to represent the operational status of weather 

sensors: yellow for storm cells, red for action alert, blue 

for operational, and black for not-operational. The text 

of airport codes is black for the yellow background and 

white for red, blue, and black backgrounds. 

Among the four colors that identify the weather status 

of an airport, red and black have multiple meanings in 

other components of the ITWS display. Red is also used 

to draw attention to action alerts. However, it is not effective for attention due to its low luminance. In addition, 

red is used to segment element titles. This color usage is 

against the convention that red should be reserved for 

alert or warning messages. 

General information

The background color is gray in most components of 

the display; however, it is slate blue in the site situation 

display. The default color is black. A total of nine colors 

are used in ITWS. However, the number of color uses 

is 24. Seven sets of color-coding are used to identify 

categories of information. One of the major problems 

with the color-coding of ITWS is that most colors are 

used to represent more than one type of information. 

Another problem is that too many colors are used for 

the purpose of attention. Since the attention capacity 

is limited, the effectiveness of each color in drawing attention is greatly reduced when several salient colors are 

used simultaneously. 

Effectiveness and drawbacks of color use in the 

three displays

We calculated the total number of instances in which 

color use is not effective for its given purpose, or the 

effectiveness depends on other attributes. That is the 

number of times “NE” and “D” appear 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” occurs in the six right-most 

columns in each table. These two numbers together can 

reflect the overall effect of color use in a display. Figure 

1 shows the results. The upper and lower panels indicate 

effectiveness and drawbacks, respectively. From left to 

right along the horizontal axis are the three decision-support displays: URET, TMA, and ITWS. The vertical axis 

of the upper panel represents the number of “NE” and 

“D;” the vertical axis of the lower panel represents the 

number of “Y” in drawback factors. Figure 1 indicates 

that both URET and ITWS have instances where the 

use of color is not effective. Moreover, all of the displays 

have a number of color usages that may negatively affect 

task performance. ITWS has an extremely high number 

of “NE” and “D.” That is partly because ITWS uses too 

many colors to draw attention or to label categories of 

information. When too many colors compete for attention, typically, none of them gets attention. Similarly, 

having too many color categories is equivalent to having 

no category. 

Color complexity in the three displays

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 & Schroeder, 2006). Figure 

2 shows the three indices for each of the three displays. 

The top, middle, and bottom panels correspond to the 

numbers of colors, color usages, and sets of color-coding, 

respectively. In each panel, the vertical axis represents the 

corresponding index. The three displays are listed along 

the horizontal axis from left to right (URET, TMA, and 

ITWS). The dashed horizontal line in the top and bottom panels each represents a saturation number beyond 

which the effectiveness of color begins to decrease, if not 

completely diminish. The saturation number of colors 

is six and the number for sets of color-coding is three, 

inferred from the literature (Carter, 1982; Cummings, 

Figure 1: Effectiveness and drawbacks of color use 

in three ATC displays (URET, TMA, and ITWS).The 

vertical axis of the upper panel represents the 

number of ineffective color use, and the lower panel 

represents the number of color use that negatively 

affects ATC task performance. 

0

10

20

30

40

No. of ineffective color use

0

10

20

30

40

No. of drawbacks

URET TMA ITWS
12

Tsonis, & Xing, 2006; Yuditsky et al., 2002).Information 

about the saturation number for color uses is not available 

in the current literature. 

Figure 2 indicates that both URET and ITWS use 

more than six colors, while TMA is on the saturation 

point. The positive difference between the number of 

color uses and the number of colors for a given display 

indicates that some colors are used to represent more 

than one type of information. Therefore, a color is not 

completely correlated with a given meaning. Such coding is not efficient in conveying information. All three 

displays have some degree of such uncorrelated coding. 

In the bottom panel, each display uses color sets beyond 

the saturation line, especially the ITWS, suggesting 

that the effect of color is not optimal. Overall, the three 

auxiliary displays have greater color complexity than the 

radar displays (Xing, 2006), suggesting a general lack of 

human factors considerations in the development and 

evaluation of decision-support tools. 

Color consistency across displays

As mentioned in the introduction, since a controller 

typically uses several displays, it is important to make 

the color-coding consistent across displays. Once we 

documented the color-coding for each display, it was 

easy to check the color consistency, given that the same 

format was used to document color use in each display. 

We utilized the following procedure to check color consistency across displays:

1) Identify the display-wide color information: background colors, default text / graphic colors, and alert/ 

emergency colors;

2) Identify the meanings of each color that is co-used in 

the related displays; and

3) Identify the colors of each displayed element that coexist in the related displays.

To demonstrate how to use this procedure, we applied 

the procedure to assess the color consistency between 

URET and DSR (URET is intended to be used along 

with DSR). The results are shown in Table 4. The rows 

of the table represent the items to be checked, and the 

columns are the displays and the consistency. Each cell 

in the table is filled with the information presented in 

the color documentation tables of the displays.

Display-wide color use

The background color is dark blue/black for DSR and 

gray for URET (inconsistent). However, since controllers 

can adjust the background color of DSR, it is difficult 

to make the background color of URET consistent with 

that of DSR. 

The default color for presenting information in the 

normal status is green for DSR and white for URET 

(inconsistent).

The color used for alert/emergency information 

that requires immediate attention is red on both DSR 

and URET, so this color is used consistently across the 

displays.

Meaning of common colors

Three colors are used in both DSR and URET: red, 

green, and brown. Red is used for conflict alert in both 

displays; green is used as the default color in DSR, but it 

represents non-conflict flight plans evaluated by URET, so 

it is not consistently used; brown is used to indicate the 

current flight altitude in DSR, yet it is used to identify 

aircraft that do not have tracking data in URET; so the 

meanings are inconsistent. 

Colors of common elements

The only common element displayed in both DSR 

and URET is the conflict alert. The same color red is 

used for this purpose. 

It is desirable that all the cells in the “Consistency” 

column are filled with “Yes.” However, that is not the 

case for most displays. When a cell is marked as “No,” 

the developers should assess the operational effects of 

the inconsistency. If there is a high probability that the 

inconsistency may lead to misinterpreting critical information, then the color-coding needs to be modified. In 

other instances, the inconsistency may lead to mild consequences such as increasing visual fatigue and controllers’ 

unwillingness to use an auxiliary display. 

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

URET TMA ITWS

Figure 2: Color complexity in three ATC displays 

(URET, TMA, and ITWS). The top, middle, and 

bottom panels correspond to the numbers of colors, 

color usages, and sets of color-coding, respectively. 

In each panel, the vertical axis represents the 

frequency index. 
13

Table 4: Assessment of color consistency between DSR and URET 

Items to be checked DSR URET Consistency 

Background color Dark blue / black Gray No 

Default color Green White No 

Display-wide 

color use 

Alert/Emergency Red Red Yes 

Meaning of 

common color 

Red Conflict alert Conflict alert Yes 

Green Default color Non-conflict 

plans evaluated 

No

Brown Current altitude 

in flying-out 

window 

Listed aircraft 

with no tracking 

data

No

Color of 

comment 

element

Conflict alert Red Red Yes 

Notice that we did not take the graphic tool of DSR 

into the consideration of color consistency. The reason is 

that the controller may choose one of the four colors to indicate a special flight region in the airspace. Theoretically, 

a controller can always choose a color that does not cause 

inconsistency with other color uses in the displays. 

DISCUSSION AND CONCLUSIONS

This report presents the results of a color analysis of 

three auxiliary ATC displays. The results allowed us to 

compare the use of color and to examine color consistency in a controller’s workstation that may consist of 

several displays. For instance, an en route controller may 

use both DSR and URET. By comparing their colordocumentation tables, we can quickly ascertain several 

key differences between the two displays. For example, 

the two displays use different default colors; the DSR 

default color is green while URET uses both white and 

black for default text. 

An immediate effect of inconsistency in background or 

default colors is the increase of visual workload for users. 

The visual system devotes more activities to responding 

to differences in visual inputs than to the absolute value 

of the inputs. Therefore, the brain responds strongly 

to the onset and switch of colors but only weakly to 

the static presence of color. Since the background and 

default colors represent a majority of the visual stimuli 

in a display, switches between colors generally trigger 

brain activity, which can increase visual fatigue, reduce 

brain resources devoted to important information, and 

lead to a higher probability of missing critical messages 

that onset simultaneously with the switches. To better 

understand these consequences, imagine the situation 

where each paragraph of this report was printed with a 

different text or background color. 

Inconsistency in color-coding can also lead to missing 

or misinterpreting color-coded messages. Inconsistent 

color-coding increases information uncertainty; thus, the 

brain’s representation of the meaning of a color can be 

biased (Green & Swets, 1988). Such biased responses can 

affect controllers’ decision-making. For example, red in 

a primary display is used for alert and warning. If some 

supporting displays use red frequently for non-critical 

information, the alert level of the brain’s response to red 

would be reduced. When a controller shifts his attention 

from an auxiliary display to the operational display, a red 

alert message may not trigger significant alert responses 

in the brain. Thus, color-coding for mission-critical messages should be consistent across displays.

The ideal way of assuring color consistency in and across 

displays is to ensure that one color has a single distinct 

meaning. However, this is difficult to achieve in reality 

because of the complexity of ATC displays. Sometimes 

it is necessary to use one color for different meanings. 

When consistency cannot be achieved, a compromise 

solution would involve compatibility. That is, if a color 

is used for multiple meanings, the meanings should not 

conflict. For example, if red is used for multiple meanings, each should be to gain attention or alert. The same 

principle applies to other aspects of the integration of 

new technologies (Cardosi, 2003). 

In summary, this report provides an example of evaluating and documenting the use of color in ATC displays. 

The results also reveal a general lack of human factors 

considerations in terms of color use in the design and 

evaluation of ATC technologies. We encourage ATC 

technology developers and interface designers in ATC 

facilities to perform similar evaluation and documentation, as we did in this study, to improve the usefulness 

and effectiveness of their technologies. 
14

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