In order to understand what happens, let's consider for a moment why
it's called a "red object" to begin with. The reason it's called "red" is that
whenever the light shining on it contains any red light, the object absorbs
light of any other colors, and only red light remains to bounce off of it toward
your eyes. Since most light contains plenty of red ... such as sunlight or the
light from an electric bulb ... the object usually looks red when you see it.
In the rare event when the light illuminating it has no red in it ... such as the
situation you describe in your question ... no light remains to bounce off of
the object to your eyes, since the object absorbs any light that's not red.
When that happens, the object appears black.
