The reason why the room was pink was because on black and white film, hues of red become dark shades of black. Pink is the perfect balance to give it that dark creepy grey.
A related fun fact: while old black and white film was under-sensitive to reds, it was correspondingly over-sensitive to greens. Actors whose characters were meant to have unnaturally pale complexions - like Morticia Addams - would often take advantage of this by wearing makeup with a green base tint in order to make their faces “pop”. This is where the modern trope of cartoon vampires having green skin comes from.
once again, this is not true. even without knowing the science of b&w photography, you can see right here that the pink wall is not a ‘dark black.’ it is a bit lighter than what a red is on the Grey Scale, a medium gray. green and red are nearly indistinguishable when shooting black and white, which us shooters need to know because contrast will NOT be there if you use them together.
if you want something dark, you pick a dark color, like purple. if you want red or pink to look dark, shoot b&w film using a bluish filter.
to me, it seems the set designers/director/DP/DoP actually wanted a low-contrast set; note in b&w how it all blends together except where the lighting is low. and i’d guess that would be so that the characters, who appear dressed all in black with black hair, can pop and not be lost in the black and white set.
another reason classic ‘hollywood lighting’ always had a hard, hard, rimlight. so that the characters did not ‘melt’ into the background when viewing in the days of b&w.