How do you make a red dress black by using light?

Simply illuminate it with a source of light that has no red in it.

A "red" dress is called "red" because that's the only color of light that it does not absorb.

When "white" light ... which has all colors in it ... shines on the dress, the dyes in the

fabric absorb all colors in the light except red. So any light that bounces off the dress

and into your eyes is red light. If there's no red there to begin with, then there's nothing

to bounce off the dress toward your eyes, and the dress appears black.