One of the best ways to achieve consistency in either a single painting or in designing an entire show, is to decide on a palette of colors to utilize, and then to stick to that palette.
I'll be doing the actual costume renderings (illustrations) in graphite and oil paint, so it made sense to use oils now when simply playing around with color. And this way I'll know exactly what colors to mix with and restrict myself to when I actually do the renderings. I could probably limit my initial palette even more, but I shouldn't get too crazy using these: Titanium White, Cadmium Yellow, Yellow Ochre, Cadmium Red, Venitian Red, Burnt Umber, Ultramarine Blue, and Cerulean Blue... I like to mix my own black using equal parts Burnt Umber and Ultramarine Blue.
My main visual inspiration for overall color themes was a photo of part of the ceiling and a chandelier in Versailles. I printed the photo out, pasted it to a sheet of paper canvas, and painted swatches around it. Some of the swatches I painted over several times, and I'm still not %100 sure the palette here is final, but this the general direction I want to take it. (adding, of course, metallic gold and silver... lots and lots of gold and silver)