Very nice poses. The coloring is simplistic but works very well. I would suggest paying more attention to your line work while shading and don't be afraid to push it further. Show some shading and highlights where you've indicated the muscle details (like the abs) with color and their anatomy will really stand out. You might also want to try some lighting effects with that fire.
But it looks pretty cool as is, because the colors complement the line art instead of overwhelming it.