Mr Light wrote:
Well most of the Corps are takes on pre-existing concepts so it's not so bad. Yellow was always there (yellow impurity, Parallax). Blue is a splinter of Green. Red is taken from the 1980s Alan Moore stories. Purple has been around forever (Star Sapphire). Orange is from the Vega Sector right where they've been forbidden to enter for decades of continuity. So really Indigo is the only one out of scratch, right?
Blue is also from scratch. While it's a splinter of Green, it only recently made its debut, unlike the Qwardian rings and the Star Sapphire gems.
(by the way, I'm completely tickled that the powers that were created in the Silver Age: Green, Sinestro, and Sapphire, are the ones leading the newer colors into battle.