Well, I had about four or five character concepts myself that I can't make work in this game due to the limitations of the costume system. The answer is 'too bad'. This isn't a game that boasts complete customization.
It's based on your powerset. Nature seems to color things red and black, Ice colors things blue and white, etc.
You're asking about your weapon abilities right? The color of the swipe (for melee) and beams/bullets (for long-range) are determined by your powerset.
There is much more customization in the end when you can pick up drops that allow you the styles of the main heroes and villains and other ones that are completely inaccessible when you start the game. It kind of sucks that you have to earn it, but at least they didn't make it terribly difficult or tedious (like Champion Online's kill 50,000 of this one enemy type to unlock the helmet for just that character's use alone).