Take a peek at a color wheel:
http://www.color-wheel-artist.com/basic ... wheel.htmlNow according to color theory, colors that are opposite from each other go well together, as well as colors that are adjacent to one another. It is naturally pleasing to the eyes.
Grey is very close to purple, so you should use purple, red and orange with Ghoulia.
Pink and Green go very well together also, so use Draculaura with the green.
I would get some more shades of the green and orange, it'll look so awesome when you are done!
Have you ever seen the homestuck trolls? Their color scheme is grey and orange gradient, they look really nice.
http://browse.deviantart.com/?qh=§i ... tuck+troll