There is absolutely no way that a white man could play Porgy.
I'm sure the man may have wanted to sing the role, but I'm sure NO one thought that it was a good idea, especially at that time.
And Gertie, Carousel with Audra was color blind casting - she had a white husband, and children of different nationalities.
Kiss Me, Kate, was not color blind casting. It was non-traditional casting, as Brian Stokes Mitchell is not white, which is what we are used to seeing. And seeing as race has nothing to do with Kate, there was nothing to be color blind about.
Personally, I think I have too much bloom.