How do people perceive white color

Apparently the physical world is colorless. Humans perceive light of a certain wavelength between 400 and 700 nanometers as colors. In the retina of the human eye there are color-sensitive visual cells, called cones, of 3 different types. They are sensitive to 3 different wavelength ranges of light, namely short-wave, medium-wave and long-wave light. The cones collect the color rays of their wavelength that fall into the human eye and pass them on to the brain, where the actual color sensation is then created (see the following illustration).

Light and color sensation

A light source emits energy beams (1), these fall on matter and are partially absorbed (2). The reflected light rays reach the eye as a color stimulus (3) and are projected onto the retina (4). The organ's own energy impulses are conducted into the brain via the nerve tracts (5). This is where the actual color sensation arises (6).

We see short-wave light as blue, medium-wave light as green and long-wave light as red.

If light is composed of 2 different wavelengths, we see cyan with a combination of short and medium wave rays, yellow with medium and long wave light and magenta with a mixture of long and short wave color rays. We perceive light that is composed of all 3 wavelengths with full intensity and equal proportions as white. If no electromagnetic waves from the color spectrum hit our eyes, the color perception is black.

So there are 8 different extreme color sensations that our human eyesight is sensitive to. They are the cornerstones of color perception and are therefore also called primary colors.

[Color theory / color theory]

© 2002 Ingrid Crüger, Fraunhofer IPSI
Above: from Harald Küppers "School of Colors. Basics of Color Theory for Computer Users and Others" dumont pocket books