Chromatics is the science of color. Isaac Newton showed that white light is composed of many different colors. This can be seen with a prism; a rainbow exploits the prismatic quality of raindrops.
Newton also showed that "the colors we observe are the result of how objects interact with the incident, already-colored light, not the result of objects generating the color." [1]
Most people are trichromats, meaning their eyes have photorecptors for red, blue and green, but 2-3% of women (so far it has been seen in women only) are tetrachromatic. In addition to the primary colors they have another type of cone in between the red and green. Normally trichromatic people can differentiate about one million colors. Tetrachromats can differentiate upwards of 100 millions colors.[2]