Guess I never read that much into Arthur. Always thought the Jewish girl looked a lot more black than The Brain. I just thought of them as a bunch of talking animals. Considering that Marc Brown is white I didn't think it meant anything. BTW, my oldest son says he wants to make a fairy tale restaurant like the one in the D.W. the Picky Eater episode.
I never noticed either until, no joke, the brain celebrated Kwanzaa (Crackzaa) all the while talking about his heritage, and Francine (impoverished, Jewish, female, mega-athlete) went to her relative's bar mitzvah, or bat mitzvah.