In a DARKroom, any light that is in there by definition should be SAFE. Therefore, you will probably want to have the best reflectance possible in the wall paint to make the room as bright as possible. In every darkroom I've had over the years, the walls were always white, usually glossy latex so it could easily be wiped down -- especially around the wet area. In the dry area, it does not matter if it's matte or glossy.
But I would definitely go with pure white unless you just have a burning desire for a particular color. Keep in mind, of course, that under safelights the colors will all change anyway, so white is a safe bet and any reflectances will still be the same color as the safelight.
The only place I would ever use matte black is right around the enlarger, but unless your enlarger is really throwing off a lot of light or it's a communal darkroom and people are close to each other (with little enlarger booths), I would not even use black around the enlarger. The amount of light thrown off by the enlarger will have to be quite substantial to fog your paper during the exposure when the paper is actually out.
Easy way to test for that, though, is to put a sheet in the easel, lay a coin or two in the middle of it, cap your enlarger lens, and turn it on for a minute or so, then develop the paper and see if the outlines of the coins are visible.
Congratulations on getting the darkroom! You've waited quite a while for this, so use it well!
