Silver

Take sandpaper to a mirror and find out 👀

(I would, but I’m not curious enough about this to obtain a sacrificial mirror)

Due to the imperfect nature of light reflecting being tinted by the glass and reflective material at the back (usually aluminum, but historically silver and mercury have been used), mirrors do have a slight color. Aluminum mirrors have a green tint, this is most evident in an infinity mirror setup where two face each other, as you look deeper into the reflections the green deepens and tints the image as the slight wavelength shift the glass and reflective material impart normalize the image towards green.

The colour of the thing it's reflecting