Colour is usually created by the wavelength of light reflected off a surface. A mirror though is simply a piece of glass which has had one side painted so that all the light is reflected back to give the reflection. So the colour of a mirror depends on the colour of the glass, but most are colourless 😀
I think technically a mirror is silver – a mirror is made of silver backing cover by totally transparent glass. We never see the actual colour of the mirror though, as it’s completely reflective, so you only see the reflected images.
I think a physicist would probably be able to give you a better answer though!
When we call something “red”, that means it absorbs all of the wavelengths of light other than red, which is reflected. So something’s colour is determined by the wavelengths of light it reflects. Mirrors reflect all wavelengths. So it that case, it should be considered “white”, which is what you get when all the different colours of light mixed together.
It doesn’t work with paints though. Ends up a kind of muddy brown
I think that technically the mirror is silver, although it does reflect things so well that it the original image is preserved. However, I dont agree that it is “white” as surely this would mean that the only colour that you see is white?
The muddy brown effect also works with icing… I found that out when trying to make purple from red and blue icing. I failed and got brown 🙁