Mirrors were originally created by placing a transparent, greenish glass over a reflective silver backing, which is still usually visible at the edges. This is why mirrors are often perceived as silver.
However, strictly speaking a mirror has no colour at all. Why? Because colours are created by the light that bounces off an object – if it looks red, that’s because red is the main colour not being absorbed.
A mirror, however, is designed to reflect everything and, with no colours absorbed at all, by definition, it has no intrinsic colour of its own.