Reexamination of Color 

Vision Standards, Part I: 

Status of Color Use in ATC 

Displays and Demography 

of Color-Deficit Controllers

Jing Xing 

David Schroeder

Civil Aerospace Medical Institute

Federal Aviation Administration

Oklahoma City, OK 73125

February 2006

Final Report

DOT/FAA/AM-06/2

Offi ce of Aerospace Medicine

Washington, DC 20591
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___________

This publication and all Offi ce of Aerospace Medicine 

technical reports are available in full-text from the 

Civil Aerospace Medical Institute’s publications Web site: 

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i

Technical Report Documentation Page 

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

DOT/FAA/AM-06/2 

4. Title and Subtitle 5. Report Date 

Reexamination of Color Vision Standards, Part I: Status of Color Use in February 2006 

ATC Displays and Demography of Color-Deficit Controllers 6. Performing Organization Code

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

Xing J, Schroeder DJ 

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 describes the status of color use in current air traffic control (ATC) displays. It represents the first 

step in our effort to reexamine the color vision standards for air traffic controllers. The current job-related color 

vision tests used by the FAA are based on an analysis of ATC tasks conducted in the 1980s. Over the past decade, 

many color displays have been introduced while the job-related screening tests for applicants are based on the 

earlier data. Thus, it is necessary to reexamine the current color vision standards. We first performed a 

demographic study to identify the number of controllers in the current ATC workforce with color vision 

deficiencies. The results indicated that there are 152 color-deficient controllers in eight of the nine FAA regions 

across the country. To understand how colors are being used in ATC displays and how they may affect the job 

performance of color-deficient controllers, we collected and analyzed information about color displays from nine 

ATC facilities, including three air traffic control towers, three TRACONs, and three en route centers. The main 

findings are summarized as follows: 1) All the basic colors and some non-basic colors are being used in ATC 

displays; 2) Critical information typically involves the use of red or yellow colors; 3) Colors are used mainly for 

three purposes: drawing attention, identifying information, and organizing information. Yet, none of the colors 

is used exclusively for a single purpose across facilities. The results raise questions regarding the adequacy of the 

current job-related color vision tests, given today’s task requirements. We also discuss several possible solutions 

to bridge the discrepancies between the current color vision standards and the extensive use of color displays. 

17. Key Words 18. Distribution Statement 

Color, Displays, Color Vision Deficiencies, Air Traffic 

Control

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 19 

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

iii

ACKNOWLEDGMENTS

We thank Keith Gunnell for his effort in coordinating facility visits for us. This project could not have 

been done without his help. We thank Dr. Carol Manning for her valuable comments on the manuscript. 

We also express our appreciation of the support from the following ATC facilities: ZDC, ZNY, ZNC, PHL 

Tower, DC National Tower, SF Tower, New York TRACON, Potomac TRACON, and PHL TRACON. We 

thank all the FAA Regional Flight Surgeons for providing the demographic data of controllers with color vision 

defi ciencies. Finally, we appreciate the efforts of all the FAA reviewers and editors whose suggestions greatly 

improved this report.

v

LIST OF ACRONYMS USED IN THIS REPORT

ACD . . . . . . . . Color ARTS Display

AMASS . . . . . . Airport Movement Area Safety System 

ARTS . . . . . . . . Automated Radar Terminal System 

ATC . . . . . . . . . Air Traffi c Control

ATOP . . . . . . . Advanced Technology and Oceanic Procedure 

CIWS . . . . . . . . Corridor Integrated Weather System 

CRD . . . . . . . . Computer Read-out Device

DBRITE . . . . . Digital Bright Radar Indicator Tower Equipment 

DSP . . . . . . . . . Departure Spacing Program 

DSR . . . . . . . . . Display System Replacement 

ETMS . . . . . . . Enhanced Traffi c Management System 

FAA . . . . . . . . . Federal Aviation Administration

IDS . . . . . . . . . Information Display System 

ITWS . . . . . . . . Integrated Terminal Weather System 

PRM . . . . . . . . Parallel-Runway-Monitor 

RDVS . . . . . . . Rapid Deployment Voice Switch 

STARS . . . . . . . Standard Terminal Automation Replacement System 

TDW . . . . . . . . Tower Display Workstation 

TDWR . . . . . . Terminal Doppler Weather Radar 

TMA . . . . . . . . Traffi c Management Advisor 

TRACON . . . . Terminal Radar Approach Control 

URET . . . . . . . User Request Evaluation Tool 

VSCS . . . . . . . . Voice Switching Communication System 

WSP . . . . . . . . . Weather and Radar Processor 

1

REEXAMINATION OF COLOR VISION STANDARDS I: STATUS OF COLOR USE IN

ATC DISPLAYS AND DEMOGRAPHY OF COLOR-DEFICIT CONTROLLERS

INTRODUCTION

Color defi ciency is denoted to people who have defi -

cits in color perception, with eight to ten percent of the 

male population experiencing some degree of a color 

vision defi ciency. Given that certain job tasks require 

controllers to discriminate colors, the FAA established 

color vision standards to screen air traffi c controller 

applicants. The existing standards evolved many years 

ago when the primary color-related tasks of controllers 

involved (a) the identifi cation of red and black text on 

fl ight progress strips, and (b) the identifi cation of red, 

green, and white signal lights used at airports (Mertens, 

1990; Milburn, 2004). However, during the past decade, 

there has been a signifi cant increase in the use of colors 

in ATC displays. Walking into any ATC facility, one can 

see a number of color displays. Moreover, paper strips 

are being replaced as the User Request Evaluation Tool 

(URET) is introduced in en route facilities. In fact, 

advanced computer displays have become an important 

source for en route and Terminal Radar Approach Control (TRACON) controllers to acquire information. In 

larger airport control towers, while controllers constantly 

scan the airport runways, look for approaching aircraft, 

and listen to pilots and other controllers, they still use 

several electronic displays to acquire information such 

as departure and arrival sequences, weather, and runway 

situations. Hence, it is necessary to reexamine the color 

vision standards and make sure that the standards fi t 

current job requirements. 

The nature of color use in ATC displays is complicated 

by differences in the use of colors across manufacturers 

and across ATC facilities. The rapid development of 

display technologies has made it simple to put colors 

on computer monitors. On the other hand, there are 

no standards or requirements about how manufacturers should use colors. Therefore, various color schemes 

have been used in current ATC displays. Some displays 

even allow users to defi ne their own color schemes. As 

a result, the colors used in the same automation display 

can vary across facilities. 

As the fi rst step of our effort to reexamine color vision standards, we documented color vision standards, 

examined the demographics of color-defi cient controllers, 

and collected information about color use from nine 

ATC facilities. We then analyzed the data and presented 

the results with respect to three types of ATC facilities: 

air traffi c control towers, TRACON, and en route traffi c control centers. Finally, we discuss the discrepancies 

between color use in ATC displays and current color 

vision standards for controllers. 

METHODS

We made site observations on color use in displays at 

nine ATC facilities: three air traffi c control towers, three 

TRACONs, and three en route centers. Seven facilities 

were in the Eastern Region and two in the Western 

Pacifi c Region. The facilities range from medium to 

large. In June 2004, the three towers we observed were 

ranked as 13th, 32nd, and 49th busiest; the three TRACONs were ranked as 2nd, 4th, and 15th busiest; and the 

three centers were ranked as 4th, 6th, and 18th in ATC 

activities. Two of the centers control both inland and 

oceanic air traffi c. 

At each of these ATC facilities, we performed the 

following activities: 1) learned how controllers used 

computer displays through briefi ngs provided by facility 

managers, supervisors, and technical staff; 2) observed 

how controllers used color information to perform 

tasks; and 3) recorded the colors used in displays and 

their relevance to task performance. In addition, we 

also discussed with the facility staff a number of color 

issues such as advantages and drawbacks of using colors 

in displays, the potential effect of color vision defi cits on 

task performance, etc. A list of the questions we used is 

in the Appendix of this report.

We used a digital camera to take screen shots of the 

displays. Those pictures were included as part of our 

documentation of color use in current ATC displays. 

The pictures were also used in our analysis of the potential effects of color vision defi ciencies on ATC task 

performance. 

We analyzed the data with respect to the three types 

of ATC facilities. For each type of facility, we examined 

three issues of color use: 1) The colors being used; 2) 

the frequency of use; and 3) the purposes. The answers 

to these questions provide descriptions of color usage 

by controllers and the rationale of necessaries to revise 

existing color vision standards. 
2

RESULTS

I. Current color vision standards and demography 

of color-defi cient controllers

Current color vision standards 

In 1978, the FAA began to use clinical color vision 

tests to screen applicants for air traffi c control specialist positions. The clinical color vision tests used by the 

FAA included the Pseudoisochromatic plates (such as 

Dvorine and Ishihara) and the Farnsworth Lantern test. 

The FAA initially required controllers to take annually 

recurring color vision tests. This requirement was removed 

in 1996. As the result, a controller is qualifi ed for color 

vision throughout the service period once passing the 

screening test at hiring.

Beginning in 1992, the FAA applied two job-related 

color vision tests to screen air traffi c control specialist 

applicants. Mertens and his colleagues developed these 

practical tests (Mertens et al., 1992; 1995). For en route 

controllers, the practical test involved identifying the 

colors of black and red text written on fl ight progress 

strips. For tower controllers, the test was to identify the 

colors of red, green, and white presented on aviation 

lanterns that mimicked the signal lights used in airports 

to control aircraft. If an applicant failed clinical color 

vision tests but passed job-related tests, the applicant 

was deemed qualifi ed. Mertens et al. (1990) found that 

about 10% of the subjects who failed clinical tests could 

pass the job-related tests. As a result, a certain percentage 

of controllers with mild to moderate color vision defi cits 

were able to enter the job. The practical test ensured that 

they would successfully handle the color-related tasks in 

the operational environment.

Demographics of color-deficient controllers

We searched the FAA medical Covered Position Decision Support System (CPDSS) database for information 

about color-defi cient controllers in the current workforce. 

The data were subsequently confi rmed by regional fl ight 

surgeons. As of August 2004, there were 125 color-defi -

cient controllers in eight of the nine FAA regions across 

the country. There were no color-defi cient controllers 

identifi ed in the Alaskan region. Table 1 illustrates the 

distribution of color-defi cient controllers in the nine FAA 

regions. Considering that there are more than 16,000 

U. S. controllers, the percentage (less than 1%) of color-defi cient controllers in the current workforce is very low. 

II. Status of color use in ATC displays

En route traffic control centers

ATC displays can be classifi ed into three categories according to their functionality. Primary displays, also called 

situation displays, are the ones with which operational 

controllers monitor moment-to-moment traffi c and to 

observe changes in aircraft altitude, direction, and speed 

as instructions are issued to maintain separation. Secondary displays are the part of a workstation that controllers 

use to acquire additional information to support their 

decision-making and coordination of the fl ow of air 

traffi c. Advisory displays are located at non-operational 

control areas of a facility. Some advisory displays are 

placed on the walls of the operational control areas so 

that operational controllers can easily see the materials 

while seated at their workstations. The largest collection of these specialized displays is located in the traffi c 

management section of the facility. Controllers within 

these areas are responsible for adjusting the volume of 

traffi c entering the facility’s airspace in light of existing 

weather conditions and staffi ng. 

The primary display for en route controllers is a radar 

display called Display System Replacement (DSR) for 

inland air traffi c or the OCEANIC for oceanic traffi c. 

The secondary displays include soft-CRD (Computer 

Read-out Device) and Voice Switching Communication 

System (VSCS). Some centers also have a User Request 

Evaluation Tool (URET). The advisory displays include, 

but are not limited to, Enhanced Traffi c Management 

System (ETMS), Traffi c Management Advisor (TMA), 

and Corridor Integrated Weather System (CIWS). The 

advisory displays use many colors. Moreover, keyboards 

at the workstations and the Key Selection Device are also 

color-coded. ETMS allows individual users to customize its color palette. Thus ETMS was not included in 

the analysis of color use. The same is true for VSCS. In 

addition, since the OCEANIC display is being replaced 

by the Advanced Technology and Oceanic Procedure 

(ATOP), we did not analyze color data of OCEANIC. 

The data about ATOP were not available at the time of 

Table 1. Numbers of color-deficient controllers in 9 FAA regions. 

Region ACE AEA AGL ANE ANM ASO ASW AWP AAL

Number 2 14 42 4 19 23 9 11 0 
3

our facility observations. An initial look at the ATOP 

display suggests rather extensive use of color.

Colors used in displays. First, we wanted to know 

what colors are being used in the en route displays. Vision research has shown that eight chromatic colors are 

considered as basic colors (Boynton & Olson, 1987). 

Those include red, yellow, green, blue, orange, purple, 

pink, and brown. The basic colors can be reliably named 

and have exact equivalences across many languages and 

geographic regions. They segregate well because they are 

maximally separated in color space. Among the basic 

colors, red, green, yellow, and blue are called primary 

colors because they correspond to the color processing 

mechanism in the human visual system. 

We listed the use of the eight basic colors in primary, 

secondary, and advisory displays in Table 2. In addition, the last column lists the usage of non-basic colors. 

A crossing symbol indicates that the color is used in at 

least one of the displays. Table 2 shows that nearly all the 

basic colors are used in the displays. In contrast, only a 

few non-basic colors are used. Typical non-basic colors 

include magenta, cyan, turquoise, and beige. Secondary 

and advisory displays use more colors than the primary 

displays. All of the primary colors are used in nearly all 

the display categories, with the exception of blue (blue 

is the DSR background color). 

Frequencies of the colors being used. Next, we estimated how frequently the colors were used in the en route 

displays. The estimation was based on color-coding. For 

example, since URET used red twice in its Aircraft List, 

once in the Graphic Display window, and once in the Plan 

Display window, we counted that red was used four times 

in URET. The estimation also considered the luminance 

factor of colors. Again, taking URET as an example, in the 

Aircraft List red represented a confl ict that was predicted 

to happen within the next fi ve minutes, while a muted 

red (lower illumination) represented a confl ict that was 

predicted to happen if the controller took other expected 

actions fi rst. So, red was used twice here. 

For each color category, the frequencies of its usage 

were summed across all the displays in the three centers. 

Figure 1 shows the histogram. The vertical axis represents 

the frequency with which a color was used in the en route 

displays. The horizontal axis represents individual colors, 

with red, green, yellow, blue, purple, orange, brown, 

pink, and non-basic colors, from left to right. Two bars 

are plotted for each color; the bar on the left is the total 

number of colors used across all the en route displays, 

and the bar on the right indicates the number of colors 

used in primary displays only. The results show that red, 

green, and yellow are used most frequently. This is especially true in the primary display. At present, the DSR 

display uses colors only for its graphic tool and weather 

information. Among the non-basic colors, cyan is used 

most frequently. 

Notice that we treated the results in Figure 1 as 

estimates instead of accurate calculations. Two factors 

contributed to the estimation: 1) We did not observe 

some infrequently used windows of displays. For example, 

URET had seven windows but we observed that controllers only used three of them and rarely used the other 

four. Therefore, we did not collect data from those four 

windows. 2) There were other advisory displays that were 

not available in the three facilities we visited. Therefore, 

this analysis provided us with a qualitative, rather than a 

quantitative, description of how often colors were being 

used in en route facilities. 

Purposes of color use. For each color we observed 

in the displays, we identifi ed the purpose of its use. We 

found that colors were used for one of the three purposes: 

1) Colors were used to draw attention. Because the basic 

colors are more salient than non-basic colors, they are often 

chosen to encode information that requires immediate 

attention, such as an alert or emergency. 2) Colors were 

used to identify certain types of information so that 

Table 2. Colors used in en route displays. 

 Red Green Yellow Blue Purple Orange Brown Pink Others

P X X X X X X 

S X X X X X X X 

A X X X X X X X X 

P = Primary displays 

S = Secondary displays 

A = Advisory displays 
4

searching for the information in complex scenes could be 

completed more effi ciently. In this case, each color has a 

distinctive meaning. For example, a controller may use a 

yellow outline to indicate a restricted fl ying zone on the 

DSR. The distance of an aircraft to that zone can then 

be displayed in yellow. The controller can identify the 

distance easily by searching for the yellow-colored text. 3) 

Colors are used to organize information by segmenting a 

complex scene into objects so that controllers can easily 

use displayed information. In this application, controllers 

do not have to remember the meaning of colors. Based on 

these observations, we can thereby classify the purposes 

of color use into three categories: Attention, Identifi cation,

and Segmentation. 

Other than these three purposes, there are many situations where colors are used for no apparent reason. For 

example, we observed that some text was gray, dark green, 

blue, or another color. Those colors could be replaced by 

other colors without causing any operational diffi culties 

for controllers who have normal color vision. However, 

the “no-purpose” has the potential to cause trouble for 

color-defi cient controllers. For example, controllers who 

have defi cits in perceiving red or green colors would have 

diffi culties in reading green text written on a dark red 

background, because both green and red appear yellowish brown to them. It is desirable that a color should be 

used only where it has a functional purpose. Unfortunately, display manufacturers do not always follow this 

principle. Moreover, if controllers are allowed to set their 

own color palette, this could cause problems for them 

or their supervisors.

Here we use the Aircraft List of URET as an illustration 

of how the purposes of color use are determined. Figure 

2 is a snapshot of the Aircraft List. The columns with 

the boxes on the left-most side of the window indicate 

fl ight status, encoded with red, muted red, yellow, muted 

yellow, cyan, and brown. In the fi rst column, the boxes 

may turn into red or muted red. Red represents predicted 

loss of separation within less than fi ve minutes. Muted 

red represents predicted loss of separation if the controller takes other expected actions fi rst. Therefore, both red 

and muted red serve as alerts that require the immediate 

attention of controllers. In the second column, yellow 

means predicted confl ict coming between 5-12 miles. 

Thus, yellow requires attention as well. While the yellow 

and red colors are to draw attention, each of them has 

different meanings, and controllers associate the color 

with its meaning. Therefore, we classifi ed the purposes 

of these colors in both the Attention and Identifi cation

categories. The cyan color in the third column of boxes 

indicates aircraft on a confl ict route. The brown color 

means that auto-prediction may not be available because 

of no tracking data for the aircraft. Unlike red and yellow, 

these two colors do not require controllers’ immediate 

attention. Controllers only use the colors to identify 

relevant information. Thus, we classifi ed the purposes of 

cyan and brown in the Identifi cation category. 

We identifi ed the purposes of color use and summed 

the results across the en route displays. Figure 3 shows 

a histogram of color-use purposes. The upper, middle, 

and bottom panels correspond to Attention, Identifi cation,

and Segmentation, respectively. In each panel, the vertical 

red green yellow blue purple orange brown pink others

Colors used in en route displays

30

25

20

15

10

5

0

No. of colors

Figure 1. Frequency of color use in en route displays. The vertical axis represents 

the frequency of color use in the en route displays. The horizontal axis represents 

colors (red, green, yellow, blue, purple, orange, brown, pink, and non-basic colors, 

from left to right). Two bars are plotted for each color; the bar on the left is the total 

number of times a color is used across all displays, and the bar on the right 

indicates the number of times a color is used in primary displays only.
5

red green yellow blue purple orange brown pink others

Colors used in en route displays

20

10

0

20

10

0

20

10

0

No. of colors

Attention

Identification

Segmentation

Figure 3: The purposes of color use in en route displays. The upper, middle, and 

bottom panels correspond to Attention, Identification, and Segmentation, 

respectively. In each panel, the vertical axis represents the frequency that a color is 

used for the given purpose. The horizontal axis represents the individual basic 

colors and non-basic colors as one category. 

Figure 2. An example of the URET Flight Strip List display.
6

axis represents the frequency of a color used for the given 

purpose. The horizontal axis represents colors, with red, 

green, yellow, blue, purple, orange, brown, pink, and 

non-basic colors (from left to right). The results show 

that, while red is often used for Attention, it is also used 

for Identifi cation and Segmentation. Ideally, red should 

not be used for non-critical purposes, because the colors 

used for Attention should not be used for Segmentation

or “no-purpose.” Many guidelines for color use in visual 

displays have recommended that red should be reserved 

only for the most important information. However, that 

is not the case with en route displays. Comparing the 

upper and bottom panels, we see that red, green, and 

yellow are more frequently used for Identifi cation than 

other colors. 

Notice that the results about color use in en route centers 

are based on the fact that URET is in use in these facilities. We need to point out that only a limited number of 

en route facilities currently use URET. For those centers 

not using URET, the use of color in secondary displays 

is not as extensive as presented in this section. 

TRACON

Operational controllers in a TRACON work with 

their primary displays to maintain separation between 

aircraft. They also frequently use secondary displays to 

acquire information and communicate with others. In 

addition to the operational control positions, each facility usually has some positions for supervisors and special 

designated controllers. For example, a TRACON may 

have several controllers assigned to the positions where 

the display is a Parallel-Runway-Monitor (PRM) tool. 

There are other advisory displays from which operational 

controllers acquire information, such as weather displays. 

The advisory displays vary from facility to facility. The 

primary display in the TRACON environment used to be 

the Automated Radar Terminal System (ARTS) or Common-ARTS. Now they are being replaced with a Color 

ARTS Display (ACD) or Standard Terminal Automation 

Replacement System (STARS). The secondary displays 

include Information Display System (IDS),t or ACE-IDS, 

and the communication system called Rapid Deployment 

Voice Switch (RDVS). Advisory displays include ETMS, 

ITWS, PRM, and DSP (Departure-Spacing-Program). 

These displays are all color-coded. As mentioned earlier, 

ETMS is not counted in the following analysis. We also 

did not include RDVS in the analysis. While RDVS used 

colors, information is precisely encoded by locations, so 

controllers primarily use location cues to acquire information and they ignore colors. 

Colors used in TRACON displays. Table 3 lists the 

use of eight basic colors and other non-basic colors in 

primary, secondary, and advisory displays; in the same 

format that was used in Table 2. The result shows that 

all the basic colors but pink are being used in TRACON 

displays. The non-basic colors include magenta, cyan, 

turquoise, beige, and others. Advisory displays use more 

colors than primary and secondary displays. The four 

primary colors are used in all display categories. Thus, 

TRACON controllers should be able to recognize at least 

those four colors. 

Frequencies of the colors being used. For every color 

category, the frequency of its usage is summed across 

the displays in the three TRACONs. Figure 4 shows a 

histogram, with the same format as that of Figure 1. The 

vertical axis represents the frequency of color use, and 

the horizontal axis represents individual colors. The bars 

on the left show the color usage for all the TRACON 

displays; and the ones on the right indicate the number 

of times a color is used in the primary displays only. The 

results indicate that red, green, and yellow are the most 

frequently used colors. Compared with the data for en 

route displays (Figure 1), TRACON displays use colors 

more extensively. Another difference between TRACON 

and en route displays is that the primary TRACON displays use many non-basic colors, most of them associated 

with the STARS system.

Purposes of color use in TRACON displays. We 

identifi ed the purposes of color use for TRACON displays 

and summed the results by colors and purposes. Figure 

5 shows the histograms of color-use purposes, with the 

same format as that of Figure 2. The upper, middle, and 

bottom panels correspond to Attention, Identifi cation, and 

Segmentation, respectively. The vertical axis represents the 

frequency of a color used for the given purpose, and the 

horizontal axis represents colors. Figure 5 indicates that, 

while red is used a majority of the time for Attention, it 

Table 3. Colors used in TRACON displays.

 Red Green Yellow Blue Purple Orange Brown Pink Others

P X X X X X X 

S X X X X X 

A X X X X X X X X 
7

is also used for Identifi cation and Segmentation. On the 

other hand, many other colors are also used for Attention. 

Thus, it is diffi cult for a controller to associate specifi c 

colors with critical information. This problem could 

become more severe for color-defi cient controllers. These 

color schemes imply that controllers should be able to 

distinguish all the basic colors and some non-basic colors to use the displays as assumed by manufacturers. In 

addition, TRACON displays use colors frequently for 

Segmentation and “no-purpose,” further complicating 

controllers’ mental association of color meanings.

Tower

Tower controllers do not use radar displays to control 

aircraft, and there is no primary tower radar display, by 

defi nition. However, they do use displays to acquire 

information. The secondary displays used in towers are 

Tower Display Workstation (TDW) and R-ACD. TDW 

is the modifi ed tower version of STARS, and R-ACD 

is ACD modifi ed for daylight illumination. An equally 

important display in towers is the airport movement 

surveillance system, either Airport Movement Area Safety 

System (AMASS) or Digital Bright Radar Indicator Tower 

Equipment (DBRITE). The advisory tools vary greatly 

across towers. Those include Information Display System 

(IDS), Weather and Radar Processor (WSP), Integrated 

Terminal Weather System (ITWS), Terminal Doppler 

Weather Radar (TDWR), Departure Spacing Program 

(DSP), and Landing Panel that displays status of airport 

surface lights. 

Colors used in tower displays. Table 4 lists the colors 

and their use in secondary and advisory displays. The 

results are similar to those of TRACONs because many 

displays used in TRACONS are also present in towers 

with slight modifi cations. For example, a tower uses 

red green yellow blue purple orange brown pink others

Colors used in TRACON displays

25

20

15

10

5

0

No. of colors

Figure 4. Frequency of color use in TRACON displays (in the same format as Fig. 1). 

red green yellow blue purple orange brown pink others

Colors used in TRACONS displays

20

10

0

20

10

0

20

10

0

No. of colors

Attention

Identification

Segmentation

Figure 5: The purposes of color use in TRACON displays (in the same format as 

Fig. 3). 
8

R-ACD if the associated TRACON uses ACD; a tower 

uses TDW if the TRACON uses STARS. R-ACD has two 

versions of color schemes, one for daylight and the other 

for nighttime. However, most controllers prefer to use the 

nighttime version, even in the daytime, because they like 

the color scheme of the daytime version better. 

Frequencies of the colors used in tower displays. We 

estimated the frequencies of each color used in tower 

displays. Figure 6 shows a histogram of color use. The 

vertical axis represents the frequency of a given color used 

in the displays; the horizontal axis represents individual 

colors arranged in the same order as that in Figure 1. 

Figure 6 indicates that all the basic colors, except pink, 

are used in tower displays. Moreover, compared with 

TRACONs and Centers, towers use a number of nonbasic colors. As a result, there are many color schemes 

in tower displays, and the schemes may be confusing. 

Essentially, we can say that many colors are equally 

important in the tower environment due to the current 

inconsistent color schemes. 

While many people have the impression that towers do 

not use many colors, surprisingly, Figure 6 indicates that 

towers use colors more frequently than TRACONs and 

en route centers do. One of the reasons for the extensive 

color use is to display weather information. Towers have a 

large variety of weather displays. Many colors are used to 

encode different levels of precipitation and wind speed.

Purposes of color use in tower displays. Figure 7 

shows the histogram of color-use purposes. The upper, 

middle and bottom panels correspond to Attention, Identifi cation, and Segmentation. The vertical axis represents 

the frequency with which a color is used for a given 

purpose, and the horizontal axis represents colors. Figure 

7 indicates that most basic colors (other than green and 

pink) and many non-basic colors are used for Attention. 

Therefore, controllers cannot rely on a single color to 

distinguish critical from non-critical information. All 

the basic colors except pink are used for Identifi cation. 

Among the non-basic colors, cyan and magenta are most 

frequently used for Identifi cation. These two colors are 

equally effective as the basic colors in target searching 

(Smallman & Boynton, 1990). Notice that in the bottom 

panel, the four primary colors are dominantly used for 

Segmentation, which introduces potential confusion with 

the Attention color schemes. For example, the color red 

could mean a wind shear warning, yet it could also mean 

nothing special such as an aircraft destination. In these 

situations, controllers have to use other visual features 

to identify critical information. 

While we presented the use of color in tower displays 

in this section, computer displays only comprise part of 

the information resources for tower controllers. The ATC 

tasks in control towers include identifying aircraft movement through the red, green, white, and blue lights at 

night or during low-visibility conditions. Controllers also 

need to distinguish between aircraft based on logos/colors. 

Taking those situations into consideration, the actual use 

of color by tower controllers is more extensive than what 

was reported in this section. 

III. Experiences and preferences in color use

At each facility, we discussed a number of color issues 

with the facility staff including controllers, supervisors, 

managers, technical support engineers, and quality 

red green yellow blue purple orange brown pink others

Colors used in tower displays

30

25

20

15

10

5

0

No. of colors

Figure 6: The frequency of color use in Tower displays. The figure is in the same 

format as that of Figure 1. 
9

 assurance analysts. While we did not systematically collect data from them, through discussions we acquired 

information about their experiences and preferences 

with color use. Next are some issues in which we received 

consistent opinions from the facility staff. 

1) History of color use

Except for the new Potomac TRACON, most facilities have about ten years of experience with using some 

color displays. In particular, there has been a substantial 

increase of color use in primary displays during recent 

years. At terminal facilities, monochromatic ARTS displays are being replaced with ACD and STARS. At en 

route facilities, DSR has adopted moderate color-coding 

and will use more colors in the datablocks. URET has 

been deployed at several en route centers in recent years 

and will continue to be deployed. 

2) Reaction to color use

The overall reaction to color use is positive. Controllers 

and supervisors like color-coding because it saves time and 

sometimes makes their tasks easier. On the other hand, 

they acknowledged that color-coding was not necessary 

in many situations, and they could not take advantage 

of some color-coding.

3) Operational errors associated with color use

None of the staff we talked with was aware of any 

operational error specifi cally associated with a controller’s 

color vision defi ciency. However, some facilities did 

report operational errors associated with color-coding. 

For example, in two TRACON facilities, ARTS Color 

Displays used different colors to represent controllers’ 

own and unowned aircraft. This scheme, by focusing 

controllers’ attention on own versus unowned aircraft, 

could cause loss of aircraft separation in certain circumstances. Informal analysis at one facility suggested that 

about one-third of their operational errors might be 

related to such color use. 

4) Text readability

All of the staff members agreed that good text readability was crucial for controllers. Text should be read 

quickly in an error-free manner. Low text readability was 

unacceptable for effective task performance. However, we 

observed a number of situations where highlighting text 

with colors resulted in lowered text readability. 

5) Effect of color deficiencies

Until very recently, most staff members were not 

aware that color defi ciencies could potentially affect 

task performance associated with using color displays. 

After we explained how color displays might appear to 

a color-defi cient viewer, about half of the staff agreed 

that color defi ciencies could have a negative effect on 

task performance. Others thought that color-defi cient 

controllers could use redundant cues to get around the 

problem.

6) Complaints about color use

One of the major complaints about color use was using red to encode warning or alert messages. Red-colored 

messages in ATC displays are often not conspicuous 

enough for immediate detection. To effectively draw attention, a target has to be brighter than other materials 

on a display. However, red is dimmer than many other 

red green yellow blue purple orange brown pink others

Colors used in tower displays

20

10

0

20

10

0

20

10

0

No. of colors

Attention

Identification

Segmentation

Figure 7: The purpose of color use in tower displays (in the same format as Fig. 3). 
10

colors such as white and green in ATC displays. Several 

staff members at different facilities expressed the same 

opinion: “Don’t use red for alert unless the red symbol 

is very bright.” 

7) Color palette customization

Nearly all of the facility staff were against color palette 

customization by individual controllers. The common 

opinion was that color schemes should be consistent 

across the ATC system, especially when a display is used 

to control aircraft (i.e., the primary displays). 

Since none of the staff members we talked with had 

any experience in working with color-defi cient controllers, we could not obtain direct information about the 

effects of color defi ciencies on ATC task performance. 

However, some of the opinions above provided a hint. For 

example, many of the staff members complained about 

low visual conspicuity of red warning messages. When 

viewed by color-defi cient controllers, such red signs would 

appear dark yellowish with a reduced luminance, thus 

the conspicuity would be even lower compared to that 

when viewed by color-normal controllers. Unless the red 

signs are accompanied with a fl ashing cue, the detection 

of such critical information would be impaired in color 

defi cient controllers. 

DISCUSSION

Our facility observations confi rmed that color displays 

have become a major source for controllers to acquire 

information. However, the current job-related color 

vision tests are based on the use of fl ight progress strips 

and signal lights. The traditional paper strips are rapidly 

being replaced by electronic displays at en route centers. 

Therefore, the strip-based test is no longer suffi cient for 

today’s ATC tasks. Also, given the use of color in tower 

displays, the job-related color vision test based on the 

discrimination of red, green, and white lights in the 

modifi ed Farnsworth Lanterns alone may not adequately 

fulfi ll the color-related task needs for tower controllers. 

We observed that tower controllers acquire information 

from many color displays. Given these discrepancies 

between the color vision tests and the nature of present 

ATC tasks, it is necessary to reexamine the current color 

vision requirements and make sure that they fi t the current 

task requirements. The reexamination effort shall focus 

on the criticality of color use, whether a color usage is 

associated with achromatic redundant cues, and relationships of color use with task performance. 

Given the diversity of color use in ATC displays, to 

develop new job-related color vision tests will require 

extensive research. The effort must include reviewing 

existing displays, identifying instances where color may 

be used as a non-redundant cue, assessing the criticality 

of information to safe fl ight, and assessing whether the 

performance of controllers with color vision defi cits differs signifi cantly from that of color-normal controllers. 

Based on the results of the above effort, we must then 

identify the practical tests that can be used to ensure that 

applicants who enter the profession possess adequate color 

vision to safely and effi ciently carry out their duties. 

In this phase of the report, several alternatives to new, 

possibly more restricted, color vision tests are proposed. 

Next, we discuss the feasibility of those approaches. 

1) Instead of creating new job-related tests, is it possible 

to solve the color defi ciency problem through manufacturers’ effort?

Theoretically, this might be done but it is not practical. 

For example, the UK Civil Aviation Authority recommended that the chromaticity differences between the 

colors in a display should be checked with the perceptually uniform color space to make sure that colors can 

be discriminated by human eyes. This method can be 

extended to the domain of color defi ciencies, i.e., the 

colors in a display should be checked against the color 

discrimination differences of color-defi cient individuals. 

This procedure can ensure that all selected colors are distinguishable by color defi cient personnel. However, the 

drawback of this strategy is that it greatly limits the use 

of color and decreases the effi ciency of color-coding. In 

addition, it can introduce further inconsistency of color 

schemes used in existing and future displays. 

2) Is it possible to solve the color defi ciency problem by 

giving controllers the fl exibility of using colors of their own 

preference?

We observed the application of this strategy in 

ETMS. Indeed, this strategy might greatly relieve the 

color defi ciency problem. However, this strategy has 

some considerable drawbacks: 1) It causes coordination 

problems for controller supervisors. Inconsistencies in 

color use among controllers may confuse a supervisor’s 

understanding of a situation and thus interfere with his or 

her decision-making. 2) Inconsistencies in color schemes 

may cause coordination problems between controllers. 
11

When working as a team, a controller could be required 

to work on a display that uses a different color scheme 

from the one that he normally uses. Moreover, imagine 

that a color-defi cient controller needs to work on a display 

that was customized by a controller with normal color 

vision. 3) Some controllers may overuse this fl exibility. 

They are probably not aware of some principles of using 

colors in ATC displays. For example, we observed several 

cases where red was used for unimportant background 

information such as boundaries. That is contrary to the 

general design principle that red should be reserved for 

critical information only. Furthermore, some people tend 

to apply too many (more than ten) colors to a single 

display mode, while the human brain cannot effectively 

search for a particular color when there are more than 

six or seven (Carter & Cahill, 1979).

3) Can the color defi ciency problem be avoided by always 

having redundant cues?

The answer to this question depends on whether colors 

are used as primary visual cues for critical information. 

Primary visual cues are the most perceptually conspicuous features of an object. The human visual system uses 

primary cues to detect critical information without a 

searching effort. Brightness and blinking/fl ashing are the 

top choices of primary cues for visual perception. While 

color is also visually conspicuous, color scientists do not 

recommend using color as the primary cue to draw attention because of color defi ciency concerns. Moreover, 

the appearance of displayed colors can vary with changes 

in the display environment and monitors. For instance, 

colors with the same specifi cations can appear different 

across monitors. Even for the same LCD monitor, color 

appearance can change greatly when viewed from different angles. Mertens (1990) suggested that color should 

never be used for the purpose of attracting attention. 

Unfortunately, we observed many situations where colors were used as the primary cue to capture attention in 

ATC displays.

The argument here is whether the color defi ciency 

problem can be solved by always using redundant cues. 

Theoretically, color-defi cient controllers can use redundant cues such as luminance, text, shape, or texture to 

back up their color perception. However, information 

in most ATC displays is highly dynamic and complex, 

yet most ATC tasks have to be performed in a timely 

and effi cient manner. For instance, a controller often 

needs to fi nd a piece of information in a complex display 

containing multiple pieces of information during busy 

traffi c. This has to be done accurately and quickly. The 

purpose of using color in ATC displays is to reduce 

the time needed to identify important information. 

For example, a warning message in a bright red color 

can be perceived by color-normal controllers instantly. 

However, the message would appear dark yellowish 

to some color-defi cient viewers and thereby reduce 

the conspicuity required to capture attention (Brettel, 

Vienot, & Mollon, 1997). While the viewers can still 

identify the message by serially searching redundant cues 

such as texts or shapes, it takes longer to fi nd the message (Christ, 1975; Treisman & Gelade, 1980). Thus, 

having redundant cues may not always be suffi cient 

for rapidly evolving ATC tasks. Redundant cues can be 

used to avoid the color defi ciency problem only when 

they are perceptually conspicuous and can be perceived 

“at-a-glance.” 

CONCLUSIONS

In this report, we analyzed the current color use in ATC 

displays. The main fi ndings are summarized as follows: 

1) All the basic colors (red, green, yellow, blue, orange, 

purple, pink, brown) and many non-basic colors are 

being used in ATC displays. Color usage in the primary 

displays is more limited than in secondary and advisory 

displays; 2) Alert and emergent messages typically rely 

on red and yellow colors, but many other colors are also 

frequently used for critical information; 3) Colors are used 

mainly for three purposes: drawing attention, identifying 

information, and separating information, yet none of 

the colors is used exclusively for a single purpose across 

the displays. 4) In some situations, color usage has some 

potential to negatively infl uence performance. Overall, 

this study found that the use of color in ATC displays 

is more extensive than what was identifi ed and used as 

the basis for the development of the current job-related 

color vision tests. The fi ndings suggest that the existing 

job-related tests may not be suffi cient for today’s task 

requirements. Further effort is needed to bridge the 

discrepancies between the current color vision tests and 

the extensive use of color displays.
12

REFERENCES

Boynton RM, Olson CX (1987). Locating basic colors in 

the OSA space. Color Res Applications; 12: 94-105.

Brettel H, Vienot F, Mollon JD (1997). Computerized 

simulation of color appearance for dichromats. J 

Op Soc Am A; 14: 2647-55. 

Carter RC, Cahill MC (1979). Regression model of 

search time for color-coded information displays. 

Hum Factors; 21: 293-302.

Christ RE (1975). Review and analysis of color coding research for visual displays. Hum Factors; 7: 

542-70.

Mertens HW (1990). Evaluation of functional color vision requirements and current color vision screening 

test for air traffi c control specialists. Washington, 

DC: Federal Aviation Administration; Report No: 

DOT/FAA/AM-90/9.

Mertens HW, Milburn NJ, Collins WE (1995). Practical 

color vision tests for air traffi c control applicants: 

en route center and terminal facilities. Washington, 

DC: Federal Aviation Administration; Report No: 

DOT/FAA/AM-95/13.

Milburn NJ (2004). A historical review of color vision standards for air traffi c control specialists at 

automated fl ight service stations. Washington, 

DC: Federal Aviation Administration; Report No: 

DOT/FAA/AM-04/10.

Smallman HS, Boynton RM (1990). Segregation of basic 

colors in an information display. J Op Soc Am A; 

7: 1985-94.

Treisman A, Gelade G (1980). A feature integration theory 

of Attention. Cognitive Psychol; 12: 97-136.
A1

APPENDIX A

List of Questions About Color Use in ATC Displays

The questions are organized into three categories: color experience, preference of color use, and observation of 

color equipments in facilities. 

Experience:

1) How long have you had color-coded displays in this facility?

 What has been the general response?

 Positive features

 Negative features

2) Has there been any change in visual complaints (number or type)?

3) What, if any difficulties have controllers experienced in using the color-coded information? (e.g. misinterpreted 

the coding?)

4) As far as you know, do you have any controllers at the facility (in your work group) who have a color vision 

waiver?

5) If yes, have they experienced any difficulties in using the advanced color-coded displays? Nature of the problem?

6) Are there aspects of the color-coding or color symbology where color is the only way to identify a problem or 

concern?

(Are there enough redundant cues for color-coding on your display so that a color deficient controller can easily 

interpret the available information?)

7) If a color-deficit controller spends 0.5-5sec longer in noticing some color-coded information than a color-normal controller, what impact on overall task performance and safety would you expect?

8) Under what circumstances would misinterpretation of the color-coded information create a safety risk?

9) Have you personally experienced low text-readability due to color use, such as, white text on yellow background, blue text on black ground, etc.? 

Have you observed other controllers experiencing difficulties?

10) Some colors on displays appear very dark such as dark blue or dark brown. Have you ever personally experienced any problems with legibility of text using these dark colors, especially at lower levels of screen brightness? 

What about other controllers? What is your opinion on using those dark colors?

11) Do controllers typically adjust screen brightness? When do they do so and how often? (maybe during night 

shift?)

Preferences:

1) How many colors you would prefer to have on a single display before you feel it interferes with overall 

performance?

2) Are controllers allowed to customize the color–settings on the display? If so, does this present any problems for 

supervisors? Does this cause any problems during the transition when another controller assumes control of the 

position? 

3) Would you prefer to have such color customization or rather not?

4) In some displays, a single color is used to represent several different types of information (i.e., multiple sets of 

color-coding). How do controllers feel about that? Does multiple color-coding bother them? 

5) Bright colors such as red are often used to draw one’s attention. Do you feel that the use of bright colors on 

existing displays is so compelling that you might overlook other critical information?

6) Colors are used to separate information. As presently used, does this appear to assist controllers in integrating 

information? Are there instances where it seems to interfere with information processing?
A2

7) Can the colors be named easily and consistently across controllers? Have you ever experienced that two controllers name a colored sign differently?

8) Can the colors on your display be easily distinguished from each other? Are there any colors that cause confusions in naming them? Are there any colors that you would recommend not using on an ATC display?

Observation: 

1) How many monitors and keyboards are there at a controller’s workstation? 

2) Are the keyboards color-coded?

3) What are the typical view angles of controllers relative to the monitors/displays? Are there side-view and / or 

head-up views?

4) What is the typical viewing distance from a controller to the monitors/displays?

5) Are the monitors LCD or CRT? 

6) Is the facility still using paper strips?