Color Study

What is a Color Study?

A Color Study is an analysis of the proposed color combinations for an HMI to determine the usability of those colors.

The most important thing to remember is that:

• Color should never be used as the sole means of conveying information

How Our Eyes See Color

The subject of color perception is very complex and is far outside the scope this web site. Very briefly, the human eye has two types of light sensitive cells: rods and cones. The rods are most useful during low light condition: they are optimized for luminosity rather than color perception, and are better at detecting motion. The cones, however, are optimized for normal daylight. There are 3 types of cones: each sensitive to a different wavelength of light (short, medium, and long). Sometimes these are referred to as blue, green and red receptors, but that is misleading because each cone is:

1. Responsive over most of the visible spectrum
2. Most sensitive in the indigo, green, or yellow-orange wavelengths

In some people, one or more of these cone types has a reduced sensitivity to light (or may be missing altogether), which causes these people to perceive colors differently from people with normal cones. Roughly 8% of men and 0.4% of women have some sort of color deficiency.

Types of Color Deficiency

The most common types of color deficiency are:

• Deuteranopia - 1% of males - no green cones
• Deuteranamoly - 5% of males - reduced green cone sensitivity
• Protanopia - 1% of males - no red (yellow-orange) cones
• Protanamoly - 1% of males - reduced red cone sensitivity
• Tritanopia - very rare - no blue (indigo) cones

Color Usage in an HMI

It is very common to see colors used in an HMI to convey information: A motor might appear:

• Green: running
• Red: stopped

A valve might appear:

• Green: open
• Red: closed

A light panel might appear:

• Green: normal
• Yellow: alarm
• Red: shutdown

Or text might change color based on any of these conditions.

The following screenshots show some typical HMI conventions and how they might appear to people with different color deficiencies. Pay particular attention to how colors are used to indicate the following:

• Run status of motors and equipment.
• Valve position.
• Type of product carried in a pipeline
• Alarm or shutdown status.

Note that certain combinations may work with some types of color deficiency but not with others.

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Screenshots from a Color-Optimized HMI Application

This section shows 10 screenshots from an application that has been optimized for people with Deuteranopia, Deuteranamoly, Protanopia, and Protanamoly. (It has not been optimized for Tritanopia, which is very rare.) Each of the 10 examples also shows what that screen might look like to people with different color deficiencies. We have adopted the following conventions to make sure all operators can distinguish the alternative colors. And, of course, we never rely entirely on color to convey meaning.

Conventions:

• Equipment
  • On - green
  • Off - grey
• Shutdown Valves
  • Open - green
  • Closed - blinking red/white and rotated 90°
• Conditions
  • Alarm - black letters on a yellow background
  • Safety - white letters on a red background
• Alarm Summary/History
  • Unacknowleded alarm - red
  • Acknowleded alarm - black
  • Alarm return - blue
• Historical Trend
  • Background - dark grey
  • Pen Colors - cyan, green, yellow, magenta, red, blue, white, black
• Check Box
  • Black x on a yellow background
• Process Line Colors
  • As shown on the Process Lines screen
• Process variables
  • Blue on a grey window

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Chiller 1A

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Chiller 1C

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Oil Separation 1C

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Oil Storage 1A

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Oil Storage 1C

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Sales Gas 1A

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Sales Gas 1C

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Vapor Recovery Compressor 1C

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Variable Speed Drives 1