Jeanette makes an interesting point. If the matt white walls do not reflect light and she has experienced no problems then is there any basis for believing that painting the area behind the enlarger matt black helps?
If the paper is taken out of the box/papersafe when the enlarger light is off and is then underneath the enlarger light when it is turned on so is never in the path of the stray light when it escapes from either the lightbox lever or the neg carrier,then does the light escaping into the "ether" of the room affect the paper anymore if the walls are non reflective white as opposed to non reflective black?
On the other hand once it escapes from the neg carrier then surely the matt black paint cannot devour the light so to speak before it reaches the paper, were that paper to be in the light path, any more than it could if it were to be matt white. If the paper is not in the direct light path then I would have thought that whatever happens to the white light rays has the same effect on the paper irrespective of the colour of the wall and ceiling provided they are non refective.
If you have matt white walls I suppose the real test is to place paper into the easel and expose without any attempt to block stray light from any source then do the same with all stray light blocked and in the dark to simulate matt black walls and ceiling and then compare prints.
Another vote for light walls. Mine are lagoon blue. The room was not intended to be used as a darkroom when it was painted.
Imagine your darkroom with the white lights on (drying, preparing printing, mounting...): black is so depressing!
All the walls in the basement darkroom are concrete block and are painted with grey Dryloc, which has a matte finish. It's about the same shade as a grey card. No reflections, even around the enlarger, but lights up quite well with safelight or spots.
something witty and profound needs to be inserted here...
I have white walls. I did paint the walls around the enlarger black because I have never been able to solve light leaks. The black paint does make a big difference.
Also, I have used both black and white laminate countertops. Small bits seem to get lost in the black countertop and I did not like it in the end.
Were I to build the next darkroom, I would keep everything white. I would use blue tack adhesive to put black fome-cor (cheap large sheets at Staples) on the walls and ceiling around the enlarger. I would use snow white laminate countertops. I would use semigloss paint. Many advocate matte paint to reduce reflection but I think that issue is minimal. Semigloss is much easier to clean and keep dust free. I would avoid colors because I think they bias print evaluation.
Likewise, I have gray sheet laminate with no seams for flooring. While I am at it, I recommend 15/16 inch thick diamond plate nitrile foam anti-fatigue matting.
I prefer light colors except around the enlargers. If all light leaks from the enlargers are blocked, almost everything could be white. The critical areas are the easel and, to a lesser extent, the developer tray. The rest of the darkroom can well be brighter for convenience and safety.