First off, I notice it isn't shaded like an
actual pyramid (where one side is mostly dark, the other side light). Also, a thought: you might want to add that magical backlight as a light source, which could make the piece more dynamic.
I'd also like to see a little more variety added into your palette. Right now it's pretty bland what with all the plain yellow. Try mixing in some warmer colors, maybe? Or you could try out some hue-shifting, a possible way to implement the warm colors, which is the last thing listed
here.