Patrick you seem irritated man. I mean isn't this a forum for a asking questions? You make it sound like he had no right asking that. And I mean come on, he made the the question pretty clear that it was about other physical differences. I agree that sexual dimorphism also pertain to the sexual organs but that obviously wasn't the point here. Seems like now you are just trying to pick fights here.
As for the original question, I would guess, for ghosts anyway, it just has to do with the females being all round thicker and more filled in. So the females get a more filled in crest. Other coloration differeances may just be the result of genetic mutation that stuck to only one sex. But i dunno just throwing out my 2 cents