Sound off in the comments. Let me hear what you think. The one at the bottom is my current pick, not because it's the most interesting or dynamic, but because it fits the characters personality.
For those that still don't know, the story revolves around a bunch of mechanics that come across an engine that can do some crazy things, and yada yada yada it belongs to someone's machine and yada yada yada.

Shows with mecha or machinery always have mechanics that are stuck playing second fiddle, and the hero goes out and ruins the machine, and they have to come back and have whoever fix it. I thought it would be interesting if the mechanics were the ones stuck out in the danger without any heros out to save them. None of the mechanics are fighters, they don't discover some hidden power inside themselves. They're a bunch of blue collar shmucks that are just trying to save their skins. Diesel is just one of them.
The thing that always bothers me about fanservice characters (Yoko included, and I love Yoko, mind you) is that they dress like common street trash but then they act all shy and conservative and have at least one moment where their top drops off and they're all "Oh no!What are you looking at, pervert!". and when they're asked why they dress like that they always say "But it's easier to fight that way! Durrhurr!".
Diesel dresses like a floozy because she doesn't care, and she knows she has big boobs so what else are you gonna do with 'em? But she's also a mechanic, so it would be a little odd if her outfits were TOO out there.

But anyway, that's a lot of extreneous information, but color theory has a lot to do with personality. So let me know which outfits you like or don't, or if you have ideas of your own. Keep in mind the majority of the story takes place in the sky, which is why I'm wary of blues and whites.