Color Basics Part 3 – How is Color Perceived?
Objects in nature derive their color from substances they possess that absorb (or subtract) certain wavelengths of light while reflecting other wavelengths back to the viewer. For example, a red apple is really not red. It has no color at all. However, it contains substances in its skin that reflects the wavelengths of light that cause us to perceive red, and absorbs the rest of the visible wavelengths so we do not see them. The viewer (or detector) can be the human eye, film in a camera, or a light sensing instrument.
We could get into a lengthy discussion of the anatomy of the human eye, and the rods and cones contained within. Instead, we will go over the cliff-notes version in this forum. The human eye is a very complex, sophisticated piece if light sensing optics that contain, among other things, rods and cones. The rods are sensitive only to the presence of light. They are not color specific. The cones are sensitive to each of the red, green and blue wavelengths and give our minds the perception of color when light strikes them through our eyes.
(Dogs, deer, and many other animals do not possess the cones in their eyes. This is why we know that they see no colors. To them the world is a black and white TV show. It is also why deer hunters can wear blaze orange outfits in the woods without scaring off the deer. Only us people can actually see the orange. To the deer we probably look like big rocks if we remain crouched and still.)
A small number of people have color-deficient vision. This can happen if one type of cone is missing or has a defect that affects the signals it sends to the brain. The most common form is the inability to distinguish between reds and greens. These people are considered color-blind. Color blindness affects approximately 8% of men and 0.5% of women. (Isn’t it interesting that 4% of the population cannot tell the difference between a red and green traffic light?)
Since color exists only our minds, explaining the physical attributes is just part of the story. Fatigue, mood, color of surroundings, and human defects all affect the color we perceive at any given moment. Color as perceived by the human eye and brain cannot be simulated exactly by any instrument, nor can any printing process truly reproduce it.