“The human eye can perceive over a million different varieties of color, but the human brain has better things to do than name them all.”

“Newton segmented the spectrum into just seven named colors:
the classic ROY G BIV divisions.”  

“While this might have seemed arbitrary, much later research by anthropologists concluded that most cultures at least have names for

black, white, red, green, yellow and blue: 

six basic color terms typically in that order, as if there were an innate hierarchy.”

[ from Neil Parkinson, “The History of Color:  A Universe of Chromatic Phenomena”]