The temptation to say "raspberry" is really strong, but that is from a couple of other threads.

Are you going to be working alone, or sharing the space?
If alone, start out with beige/flat white. Then add areas of dark/black, where you have light sources that you don't want to affect materials. Places like behind and above the enlarger light source.
A light, neutral colour is a much, much, much more pleasant place to work when the lights are on, and you
will spend a lot of time there with the lights on.
In particular, a light coloured ceiling makes it much easier to reflect and diffuse a safelight. And you can always put a dark patch above the enlarger.