Looks great! Nice colors. The yellow works for me, though the blue and purple are a bit too close to each other I think. I know you keeped it simple and low-color, but you could maybe try to AA the purple with the blue.
Edit: Oh, Stasis beat me. And I couldn't resist to make an edit.
If you're really going for simplicity, you could make the purple and blue one color instead. 
At 1:1 view, I would never have noticed the difference. Not that 3 colors versus 4 matters, just an observation.
Nice avatar though! 
Hmmm. That dark green is not the best choice for AA I think. The piece has lost it's clean look now and looks a bit ... well I don't really know how to formulate it ... maybe 'hairy' or 'lumpy'.