Lot of people think that it is silver. It is however not correct. The video of @moffay explains it well. In effect he provided the right answer, although I was looking for the answer for a perfect mirror. This is the colour white, since we perceive something being white when all frequencies of our sunlight are reflected, and that is exactly what a mirror does, reflects everything. Each colour has its own frequency. An object we perceive as blue, absorbs all frequencies except the one for the colour blue which is reflected of the object and therefore we see the colour blue.
Lot of people think that it is silver. It is however not correct. The video of @moffay explains it well. In effect he provided the right answer, although I was looking for the answer for a perfect mirror. This is the colour white, since we perceive something being white when all frequencies of our sunlight are reflected, and that is exactly what a mirror does, reflects everything. Each colour has its own frequency. An object we perceive as blue, absorbs all frequencies except the one for the colour blue which is reflected of the object and therefore we see the colour blue.