Exactly right, AgentSmith; I just rendered the above to illustrate. There's only a white sky dome in this; no sun, no lights at all. The ball actually has a 100% level of red diffusion, but it's irrelevant because there's no lights. The only illumination 'on' the sphere and the ground plane is their blurry reflection of the sky dome above and around. The 'shadow' under the sphere isn't a shadow at all; it's just a blurry reflection of the underside of the sphere. It's the same shape as in yours (slightly different angle of view). The problem is that the reflection isn't blurry enough - it's still a discernable sphere.