Color = Difficulty

I know the title may be a little hard to understand. But what I'm wondering is what is the first game that used the same character model just with different colors to show that their tougher enemies? What is the latest game to use this cheap ploy? And what other famous games use it?
Just to give you a couple examples, Halo does it. Blue < Red < Gold < White. Which always made me wonder. Elites can found in these colors and so can Grunts, but Hunters only ever have blue armor. How badass would a white Hunter be?!
TMNT4:Turtles in Time, released in '92, had even more colors of Foot Ninjas. Almost every color in the rainbow I think. Purple, Blue, Red, Yellow, Orange, and White are the only ones I recall. There's probably more.
Just to give you a couple examples, Halo does it. Blue < Red < Gold < White. Which always made me wonder. Elites can found in these colors and so can Grunts, but Hunters only ever have blue armor. How badass would a white Hunter be?!
TMNT4:Turtles in Time, released in '92, had even more colors of Foot Ninjas. Almost every color in the rainbow I think. Purple, Blue, Red, Yellow, Orange, and White are the only ones I recall. There's probably more.