How do we perceive colors, and what’s the difference between how colors work in light versus in printing and paint?

-Karthik Gurumurthy

The human eye and brain work together to perceive color. The retina is the light-sensing structure on the back of the eye. In the center of my retina are seven million cones, which are sensitive to red, green, and blue light.

Rods located on the peripheral of the eye are sensitive to dim light and handle vision in low light. When light hits the rods and cones, complex chemical changes create electrical impulses that are sent to the brain via the optic nerve. Each eye contains about one hundred million rod cells.

White light, such as sunlight, incandescent light, and fluorescent light, is made up of seven colors. These are the ROYGBIV colors of red, orange, yellow, green, blue, indigo, and violet. Isaac Newton named these colors. Of those seven, three are considered the primary colors for light: red, green, and blue. These same three colors are used in color television.

Around 1680, Isaac Newton in England discovered that color is not “built into” an object. The red is not “in” the apple. Rather, the surface of the apple is reflecting some wavelengths of light and reflecting other wavelengths to the eye. A red apple reflects red light to the eye and absorbs the remaining six colors. We perceive only the reflected light, so we say the apple is red.

An object appears white if it reflects all the wavelengths (colors). An object is black if it absorbs all seven colors. A yellow object will reflect red and green, and absorb blue.

The primary colors for printing, paints, pigments, and dyes are cyan, magenta, and yellow. These are the inks used on rollers when color pictures in magazines and newspapers are printed. Cyan, magenta, and yellow are also used in our ink-jet printers.

Most animals have limited color-seeing capability.