Most color machine vision applications illuminate an object with a white light source. Depending on the color, the object “reflects” (scatters) differing amounts of different wavelengths, and absorbs others. The camera then measures the amount of reddish, greenish and bluish wavelengths that are present in the reflected light from each point on the object.
Loosely speaking, “white” light is light that contains a mixture of wavelengths from a wide range of the visible light spectrum. But if we try to get more precise than that, we learn that there is no single answer to the question of “what color is that object?” or “what exactly does white color mean?” because this definition of “color” is a human perception. A person’s perception of color is affected by many things such as the color of the room that they were recently in, or ways that their brain manipulated color shades. More importantly here, there are many different combinations of wavelengths of light that may appear to be the same “white” to a person and so human perception of the “color” of white light is not enough to determine suitability for the application.