It's not as if there were no 1950s SF movies in color--we could all name a bunch of them. In this case, the movie they had specific reference to was THE BLOB; the small town theater in the movie is >showing< THE BLOB, and there are scenes from that movie in this one. The movies most directly sourced are, in fact, THE BLOB and IT CAME FROM OUTER SPACE. I thought perhaps they were nodding to BRAIN FROM PLANET AROUS, too, but that seems to be more happenstance than deliberation.