Of the three primary colors, people (homo sapiens) see green best, followed by red, but we really suck at seeing blue. This page:
http://nfggames.com/games/ntsc/visual.shtm
is a nice demonstration of just how much we suck at seeing blue, especially compared to green. Most image and video compression takes advantage of this fact, and sacrifices a ton of bits devoted to transmitting the blue portion of an image.