With Anne's portrait, I think it might have been that it was done later, so it was likely artistic license. Was that portrait done in the reign of her daughter or before? Perhaps most interesting of all is the the true hair color of the wives like Catharine Howard who we really don't have a reliable portrait of, and also Anne of Cleves/ Jane Seymour because they wear headdresses in their portraits. Then again, if we could see their hair, maybe it wouldn't be the color their hair actually was, anyway. There's another lock of Katharine Parr's hair out there by the way. I saw it online, and it looks exactly like this one.