[heartwood]

There are two portraits by Allan Ramsay, full face and profile, such that if you saw a young American woman today with those features, you would think her likely part black.

She was seventeen. Later painters were probably told, make her look English.

[JayGalt]

Did you look at the many portraits at the link? The article was written in 2017 before the question of "black" was raised. 89 additional portraits from the National Gallery are here:
https://www.npg.org.uk/collections/search/person/mp00845/charlotte-of-mecklenburg-strelitz

This one is from 1761 when she was 17 years old and there is no suggestion of negroid ancestory.

[JayGalt]

https://m.media-amazon.com/images/I/918flbJ7FeL._AC_SL1500_.jpg

When you look at the above Ramsey portrait what you notice first is how poorly Ramsey portrayed the human form. Look at her neck, her shoulders, if he painted her lips a little thick it's nothing compared to how he thickened her neck and distorted her shoulders. Using this artist as the "true" representation is a tenuous position.