Conspicuity describes how well an object can be detected, or how it captures a user’s attention amongst other noise or other competing information. While this involves legibility, and readability, it also implies other display characteristics.

Color can be used to classify, label, and emphasize information displayed on a screen. When using color for these things, you need to understand that there are limits on the ability of people to process information. Understanding of how these cognitive and physiological limits effect our signal detection is very helpful in making choices for interactive design.

Opponent Processing Theory

In 1892, A German psychologist Ewald Hering theorized that there are six elementary colors that are arranged perceptually as opponent pairs along three axes. These pairs are: black-white, red-green, and yellow-blue. Each color is either a positive (excitatory) or negative (inhibitor). These opponent colors are never perceived at the same time because the visual system cannot be simultaneously excited and inhibited.

Our modern color theory stems off of this. Today, we know that the input from the cones is processed intro three distinct channels:

Color for Labeling

Or more technically, color for nominal information coding, is used to because color can be an effective way to make objects easy to remember, as well as to visually classify.

Perceptual factors to be considered in choosing a set of color labels:

Traditionally in China, red equals "life," and "good fortune," while green means "death." This is a commonly repeated example in design of the gulf of cultural differences. However, traffic signals in China are the same as everywhere else, so controls using red as stop will still work. Whatever the culprit, cultural differences of this sort are slowly eroding.

Color Conspicuity Guidelines For Mobile Devices