The ideal color scheme for a categorical color code depends on whether speed or accuracy is more important.[3] Although humans are able to distinguish 150 different colors along the hue dimension during a comparative task, evidence supports that color schemes in which colors differ only by hue (equal lightness and colorful "Saturation (color)")) should have a maximum of 8 categories with optimized stimulus spacing along the dimension. of tone,[3]​ although this would not be accessible to color blind people. The IALA (International Association of Marine Aids to Navigation and Lighthouse Authorities) recommends categorical color codes in 7 colors: red, orange, yellow, green, blue, white and black.[4]​ Adding redundant coding of luminosity and color adds information and increases the speed and accuracy of color decoding tasks.[3]​ Color codes are superior to others (letter coding, shape, size, etc.) in certain types of tasks. Adding color as a redundant attribute to a numerical or letter encoding in search tasks decreased time by 50-75%,[2]​ but in one-dimensional identification tasks, using alphanumeric or line-slant codes caused fewer errors than color codes[3]​[2]​.

Several studies demonstrate a subjective preference for color coding over achromatic coding (e.g., shapes), even in studies where color coding did not increase performance over achromatic coding[2]. Subjects reported that the tasks were less monotonous and caused less eye strain and fatigue.[2]

The ability to discriminate color differences decreases rapidly as the visual angle subtends less than 12' (0.2° or ~2 mm at a viewing distance of 50 cm),[5]​ so a color stimulus of at least 3 mm in diameter or thickness is recommended when the color is on paper or a screen.[6]​ Under normal conditions, colored backgrounds do not affect the interpretation of color codes, but chromatic (and/or low) illumination of the color code Surface color may degrade performance.[3]​.

The ideal color scheme for a categorical color code depends on whether speed or accuracy is more important.[3] Although humans are able to distinguish 150 different colors along the hue dimension during a comparative task, evidence supports that color schemes in which colors differ only by hue (equal lightness and colorful "Saturation (color)")) should have a maximum of 8 categories with optimized stimulus spacing along the dimension. of tone,[3]​ although this would not be accessible to color blind people. The IALA (International Association of Marine Aids to Navigation and Lighthouse Authorities) recommends categorical color codes in 7 colors: red, orange, yellow, green, blue, white and black.[4]​ Adding redundant coding of luminosity and color adds information and increases the speed and accuracy of color decoding tasks.[3]​ Color codes are superior to others (letter coding, shape, size, etc.) in certain types of tasks. Adding color as a redundant attribute to a numerical or letter encoding in search tasks decreased time by 50-75%,[2]​ but in one-dimensional identification tasks, using alphanumeric or line-slant codes caused fewer errors than color codes[3]​[2]​.

Several studies demonstrate a subjective preference for color coding over achromatic coding (e.g., shapes), even in studies where color coding did not increase performance over achromatic coding[2]. Subjects reported that the tasks were less monotonous and caused less eye strain and fatigue.[2]

The ability to discriminate color differences decreases rapidly as the visual angle subtends less than 12' (0.2° or ~2 mm at a viewing distance of 50 cm),[5]​ so a color stimulus of at least 3 mm in diameter or thickness is recommended when the color is on paper or a screen.[6]​ Under normal conditions, colored backgrounds do not affect the interpretation of color codes, but chromatic (and/or low) illumination of the color code Surface color may degrade performance.[3]​.