This is all about semantics, everyone has their own take on what being colour-blind means. Ms. Jaimet is right on.

For most people who think it is a good thing, it does not mean it "tells young people to see differences as negative things to ignore or erase." It means exactly the reverse, to "recognize that human variances don't have any kind of intrinsic value or place in a hierarchy."

A kid who wants to dress as an Indian Princess wants to dress as a Disney Princess who is also American Indian. She is both simultaneously. There may be no Indian Princess, but neither are there Disney Princesses outside of the Disney universe. 

And this is self-contradictory argument. Surely it is wearing the costume without the "blackface" that is incomplete and "acting as if you didn't notice what is an integral part of them", just as it would be strange to dress as Anne of Green Gables and not paint on freckles, a very integral part of the character?