We know that black objects absorb light with almost all the frequencies of the visible spectrum. This means there will not be any frequency of light reflected and falling on our retina, in order for us to see that object.
Does this mean that I am actually not seeing the black object but differentiating it from the surrounding?
Actually, black objects absorb light across visible frequencies indiscriminately, but not completely. So some light still reflects off them. This is described on this Q&A of the Department of Physics, University of Illinois at Urbana-Champaign.
But even if there was a perfectly black objects which absorbs 100% of the light that falls on it, you could still perceive it as it via the contrast to other objects around it.
