The color of a mirror is a subtle and interesting concept. Technically, a perfect mirror reflects all wavelengths of visible light equally, so it doesn’t have a color of its own—it simply shows the colors of whatever is in front of it.
However, most real mirrors are made with a thin layer of metal (like silver or aluminum) on glass, which slightly tints the reflection. This often gives a very faint greenish hue, especially around the edges, due to the iron content in the glass. So while a mirror looks “colorless,” it’s actually reflecting colors with a tiny bias toward green.