Which is the color of dark matter?

Dark matter has no color, because it's transparent, so it is invisible.

Let's see what makes a body to be black or dark in color. If the body is dark, it means that the body absorbs almost all photons of light which are falling on that body. Because these photons are not reflected back to reach the eye of the beholder, that area of space where that body is, is appearing to have no color. It means that appears black in that area in the image formed in our brains. But because other bodies around it, reflect some light and those bodies could be seen, our brains deduce that there exists a body and it is black. But if it is completely dark, then any colored bodies could not be seen and everything is black.