Well, while a show like THURGOOD or THE DIARY OF ANNE FRANK would not do well with "color-blind" casting, I think GYPSY could work. While Gypsy and many of the other characters were real people, I would bet not many people seeing the show would know what any of them actually look like, other than Gypsy and June. Besides, the show takes so many liberties anyway, I don't think it matters much.
That being said, Tonya Pinkins would be incredible. And so would Donna Murphy.
I am a firm believer in serendipity- all the random pieces coming together in one wonderful moment, when suddenly you see what their purpose was all along.