After spending more than fifty years in all kinds of studios, I really don't have a favorite wall color. The comments of those in favor of black are for the most part correct. I worked in many studios/sound stages in Hollywood that were painted a battle ship gray, they worked fine, others were black or white.
I frankly had no trouble adapting to any of them. However my preference
for a small shooting room is White, for a large, warehouse or sound stage,
gray or black can be an aid in building your light. I have never been bothered by stray light as I use "cutters" or "gobos" and screens/scrims to correct it. Or reflectors to push light into where I want it. I will completely tent an item with black velvet or use the same to subtract light as Leon Kannamer used to teach. I really don't think that wall color is very important. If one finds that a particular wall bounces light all over the place, paint it flat black, flat black actually reflects more light than gloss black. The gloss has specular highlights and the flat is more defused. I try to build my lighting to be stronger than the ambient light thus eliminating a potential problem of stray
light. I did many years ago have a studio with a sky blue cealing about 15
feet high. My first full length brides all wore blue tinted dresses until I found the culprit.