What color is the mirror?

The mirror does not absorb any light, but reflects it. It is what color it is when it is illuminated, yellow when it is illuminated by yellow light, green when it is illuminated by green, and white when it is illuminated by the sun.

The so-called color is the light reflected by the object. For example, a red dress is red, because it absorbs other colors of light, but it does not absorb red light, but reflects red light, so we can see that this dress is red.