What are you asking for, though? A genetic study proving that Khafra was actually black? You might as well ask for scientific evidence that Caesar was white.
I take that as a no, you don't have any evidence to back up your dogmatic statement. But it would be nice to at least have a mummy to test, but then we don’t have "Ra Khaf's" mummy do we?
I'm saying it's safe to assume that an individual living in Pre-conquest Egypt would probably have physical features similar to other ethic groups in the same contiguous region.
It's never safe to assume, especially in regards to a discipline that wants to be taken seriously as scientific, as Egyptology does, or for that matter, by any individual who wants what they say to be taken seriously.
Anyhow, there's plenty of evidence that the ancient "Khemitians" were a mixed people from the very beginning, (i.e. all those mummies we do
have, among other things) to "assume" that they must have been black is to trade the current political correctness for the old Eurocentric PC, both are equally suspect. And all this speculation still doesn't get us any closer to a "scientific" answer; it's all pretty much guesswork.
But more to the point, there is
a diorite statue, said by Egyptologists to be of Khafra, but the provenance is suspect, (i.e. his name isn’t written on it) so there is no certainty on the matter, and FWIW, it looks Caucasoid.
Then there's the Sphinx, said by Egyptologists to be carved in the likeness of Khafra, but again, there’s no certainty in the matter, and as pointed out already, it does look Negroid, and so these two supposed likenesses of Khafra don't even look like each other, and are clearly different people.
Bottom line is; nobody knows what Khafra looked like or what his ancestry was.