Color is light and colored objects absorb and reflect different wavelengths. Light & color are seen by the human eye because of the two types of photoreceptor cells - rods and cones - located in the retina of the eye. Rods are sensitive to light and dark; cones are sensitive to red, green & blue light and responsible for color vision. These photoreceptors convey the color of light to our brain.
When our eyes are exposed to a hue for a prolonged period, the rods & cones become fatigued. You might notice this if you are reading something on colored paper, and then look away—you often see the inverse, or complement, of the image. This occurrence can be advantageous if you are seeking the opposite, or contrast, of a color. This may be dismaying to a viewer if presented with prolonged exposure to colored screens or reading materials.
Every color has an opposite, and although individual's perceptions do vary, the range of after images seen is consistent.
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