Why are dust grey in colour?

Question

why not brown?

Answer 1

dust is made up of small particles which don't reflect very well.

The many different things which make up "dust" reflect different wavelengths of light , but the particles are very

tiny. They don't individually reflect a lot of color information to your eye. Instead, when you look at "dust" your eyes may get more information about light vs. dark than specific colors.

Answer 2

of course they catch germs and bacteria.

bacteria is very dirty and it affects the color of the dust.

why not brown?

germs and bacteria are really black and it blends the color of the dust.