A sense of depth is needed here to guarantee the viewer understands what's the front and back. The back end of the abdomen needs to be of a darker tone compared to the front.
It needs to be done in the same manner as the way you have the legs. They become darker as they recede to the background.
Speaking of legs this fellow unfortunately has lost some. I assume you're trying to build speed due to this oversight. Intended or not this is good practice to see how much you can get away with. Honestly I didn't notice at first because your understanding of balance is uncannily good. I can say the same thing with your colors.