Why do you see lemons as yellow?

Answer 1

All objects reflect the color of light that you see. Thus; lemons reflect yellow light rays, limes reflect green ones, and Oranges reflect orange light rays. On a final note, white objects reflect all colored light waves, and black objects reflect none.

With that said, the cones in your retina register these reflected light rays; thus, it makes sense that rooms without any light are black.