I think the colours work well. I would just say that the skull could do with some sharper edges. It may even work better with skull inverted to how you have drawn it. So all in white, with the lines and shading revealing the background. You could even do this by just using the eraser tool as a sharp pencil. It looks like it could also be a nice logo, perhaps with some typography included?View attachment 6849
Finally finished this, not for anything specific just for practise. Started it I think November last year then forgot about it! Just got round to finishing it this morning. I'm self-taught illustration wise (studied Graphic Design, not illustration) so any feedback welcome.