I did something similar about six months ago, and the feedback I got was, if you're going to have multiple sugar skulls in there, don't do all the same one. You have five different color combos, try doing five different designs on the skulls. And perhaps there could be fewer of them, but bigger.
I love the colors. They look great on the black.
All this being said, I am gonna look hella unoriginal when my own sugar skull designs make it onto the site in a few days. ;)
About my design