Its like when you use face paint on a person for halloween. I'll probably never be as good as you when it comes to skulls. But thats ok I wasn't going for realism this time. I wanted to do something new and fun.
The sort of pale grey blue is a good color for a skull, but if you want to go for a little more realism, use a reference. The lower jaw is way too thin, unless this isn't supposed to be human. An ear is still attatched, is it still alive?