I don't know about others but the Nostromo never seemed dingy to me. There were certain set pieces that were darker then others but some of the main areas, mess hall, cryo chamber, mother control room were white and sanitized or an off white and sanitized.
And as far as ALIEN RESURRECTION is concerned. Yes, it was beautiful to look at, but in comparison to the shitty story that's not saying much. A L I E N succeeded because the sets were so perfect they nearly didn't seem like sets to begin with. What I remember more about the first 3 films is atmosphere and character, the last was all window dressing and no substance. So, in my opinion, that's not really a win.