How did 2 good-looking, tan gypsy's have a pale, ginger kid? * Referencing Quasimodo and His Parents*

well Quasimodo didnt get much sun ..

Most likely it was a genetic mutation. Since he is misshapen and deformed it is likely that he had other genetic abnormalities, like being an albino, which would contribute to the red hair and pale skin.

lol you are right! I think that the Disney movie makers designed Quasimodo after the original character in Hugo's book.I have noticed many similarities and the most important is the red hair.In the book Quasimodo's parentage or race is not clearly mentioned,so he could be no gypsy.I guess in the disney film they wanted to emphasize Frollo's racistic character (though in the book it's not racism so much which leads Frollo to his horrible acts,but obsession and passion) in order for this movie to be also a good lesson for small kids.For that purpose they made Quasimodo a gypsy,yet inspired by Hugo's description for the designing of the character.