The key thing about the portrait on the right is that is displays a complexion that is found in Africans, and leaves no doubt that it is a black woman you are looking at, wavy red hair not withstanding. Yes there is a bit of wavy red hair showing underneath the head dress, but you have to look harder. Having seen her like this makes it a doddle to believe that a lot of royal portraits have been deliberately whitened, as shown below. It is easier to believe that this is a copy or an early original and those that we see, even those that claim to be original. I'll have to check up on its provenance.
A lot of the cues I associate with African people are evident. If you take a look underneath her eyes, the folds in the skin, don't they bring Aretha Franklin or Thomas Sankara to mind? She has that kind of Northern Ghana, Upper Volta look.
I discovered a portrait, displayed here on the right which shows her as a clearly Negro woman. It appears to be made of stained glass and the whiteness of her face is at odds with the brown of her hands. It looks like it wasn't finished, unless there is a symbolism to the whiteness of her face or she did her make up in the manner of Elizabeth I. It is quite different from the other more recognized pictures and it appears to be stored behind a glass cabinet. However good a likeness it may be, someone created that portrait believing it to be a good likeness of Margaret.