I feel that. I honestly was fucking around with the background quite a bit and then just settled on that simple gradient. I couldn't get anything going. Do you personally have any ideas? If not it's cool, I'd just really like to complete the piece and make it as dope as possible.
I'd probably try a darker color, for example the teal on the face - only even darker. And make the shape behind him a something brighter, maybe the yellow you have now.
Maybe some big brush strokes/paint textures on a lower opacity over the BG.
Just spit balling. It's your piece, do whatever suits your mood. Looks already damn good.