Perhaps it would help to look at wings of real butterflies. The thing about insects is that they don't get their colors from pigmentation like so many things in our world, but from the structure of the material. Because of this the wings of a butterfly won't reflect light quite the way you expect, but your eye still recognise the difference and that's why you're unhappy with the result. I did some studies of butterflies and other insects last summer; references that may work with the pattern you've chose to use is Monarch, and for the colors I would suggest Morpho, cause interferencial colors are the best :P