My take on it is that no one said it at all. Look at the facts, M is mixed but very light skinned and Harry is white with red hair, ie pretty much the lightest colouring you can have besides having albinism. That baby was never going to be dark, let’s credit the RF with some intelligence here, they would have been able to see that. There’s speculation because M deliberately left it open to it, by not naming anyone. They may have made an innocent comment such as I wonder who he’ll look like, but I guarantee it wasn’t some racist hateful comment.
Also, M said it in the context of it being the reason Archie didn’t get a title, i.e. there were concerns over his skin colour which is why he wasn’t given the Prince title or security. This is all total bollocks.
M is a liar, and I don’t think anyone made the fabled comment.
Edit- how have the Cambridges overdone the PR!? One pre planned engagement where William said the family aren’t racist, Kate very low key at Sarah Everard’s memorial and a Mother’s Day post... ffs.