Color Blindness

When we see different colors, we are perceiving differences in the light that is reaching our eyes. The way we see different colors is something like the way we hear different sounds as being "low" or "high." This is called pitch, and it corresponds to the frequency of the sound.

The keys on the left side of a piano keyboard make low-frequency sounds, for example, and the frequency of the sound gets higher as one plays keys further to the right. There is a similar order to the colors we see.

The colors of every rainbow always appear in the same order: red, orange, yellow, green, blue, indigo, and violet. The different colors in each part of the rainbow correspond to a different wavelength of light. Reddish colors are long in wavelength and bluish colors are shorter. And just as there are many notes on the piano, there are many wavelengths of light corresponding to different colors.

© 2005-2013 WebMD, LLC. All rights reserved.
Source article on WebMD

Source: MedicineNet.com
http://www.medicinenet.com/color_blindness/article.htm