I didn't realize this way back in the day, but as a general formula, Marvel Comics' bad guys usually wore green or purple or both. Or maybe those were the bad guys that I remember best? Dr. Doom, Elektro, Green Goblin, Dr. Octopus, Loki, Scorpion, The Vulture, etc.
Anyways...that can't be an accident. Kang is no exception - one of my favorite designs.