Our kitchen doorstop

It goes back to the apple Peter: - Light, shade, shadow, shine (reflection from the light source) and reflected light (light that has bounced of some other surface. If you have 3 or 4 or 5 of these, then it should look solid. Well done for putting shine in the eyes. The addition of shade and shadow would make it look more solid, including shade on the surface on which he is standing. I don't think you would find much reflected light as his surfaces are not very reflective. Hope this helps.

I agree with Linda, just another couple of darker tones to make it look rounder (like the Apple) ;)