Stanley's crude, brutish behavior is part of the "colored lights" of their relationship. His aggressive masculinity is something to which she is attracted; in a way, she finds his brutishness somewhat stimulating, actually.
There is actually domestic violence in their relationship (Stanley giving a loud whack on Stella's thighs + hitting her when she is de facto carrying his baby) but Stella is that submissive/docile that she easily succumbs to her husband. Given that particular time/setting of the play (after World War 2), there was a lot of turmoil (men were quite belligerent) and women were heavily dependent on their consorts (financially). Stella accepts this violence of Stanley, and even goes to the extent of saying that there must be some adjustments to make of a marriage a happy one. Stella dotes on Stanley to the point of hero-worship. Their relation borders mainly on the animalistic nature (Stanley throwing a packet of red meat, having sexual undertones + Stella crying on his lap + breaking the lights on the wedding night).