[Xurinos]

My guess: The object that does not reflect light to you ceases to exist in your vision. Nothing comes from that direction. Your brain would then attempt to compensate -- as it does for the blind spot in both your eyes -- and fill in the void, perhaps with a fuzzy version of continuity of whatever colors and textures surround the object.

[jerf]

We don't need to make wild hypotheses about what an object that doesn't reflect light looks like. It's so mundane we have a word for it: "black".

[TallGuyShort]

It would look black to a light sensor. As he says, your brain does play tricks and fill-in-the-black more than you might think. If you have a blind-spot you don't always perceive the absence of light - you may perceive what your brain is expecting. There are also disorders where it does this too much. I knew a guy who used to do things like overfill his coffee mug all the time, because the mug kept looking empty and then suddenly it was overflowing - his brain just expected the mug to stay empty.

[d23]

Wouldn't it just be dark? I think the blind spot is a different phenomenon. This would be no different than being in a pitch black room.

[Xurinos]

Maybe the critical question is: If no light at all comes from the object, is that the same as it being dark, or is it a complete lack of stimulus?

If the brain receives noise, it fills in the blanks (http://www.sciencedaily.com/releases/2000/06/000601164617.ht...). In sensory deprivation, the brain also fills in the blanks (would cite but ended up finding a ton of supporting material in a web search, including an interesting study about the effects of anxiety on amount of hallucinations).