I like watching movies from the early 30’s, the “pre-code” era. Here’s something that seems to be a significant plot point in 1933 “Ann Carver’s Profession” (profession=lawyer), but I don’t understand it. Can anyone familiar with the era explain it to me?

The defendant is a wealthy young man who’s been charged with breach of promise. That’s not a charge we hear about any more, but it used to apply to a man who had promised to marry a woman, and trusting in that promise she had sex with him. If he subsequently refused to marry her, he could be charged with breach of promise.

The thing I don’t understand is that apparently it matters a great deal whether the defendant knew that the young woman is black (“colored”). If the woman can prove he knew she was black, he could be charged as guilty. This implies that if she was passing as white and deceived him, he wouldn’t be guilty.

I don’t get it. Why would that make any difference?