The art collections of Oxbridge colleges are strange creations, growing slowly over centuries to no consistent plan. Often, the more interesting pieces end up in our possession by an accident of history. Allan Ramsay's portrait of Queen Charlotte Sophia, painted soon after her marriage to George III in 1761, is a case in point. Along with Ramsay's portrait of George III himself, it was a present from the royals to the President of St John's soon after their visit to Oxford in 1785 to attend St Giles's Fair right in front of the college.

Queen Charlotte Sophia

Queen Charlotte Sophia c.1784

Allan Ramsay (1713–1784)

St John's College, University of Oxford

It was admired at the time as an example of Ramsay's ability to convey the 'mental part', and particularly of his mastery of female portrait. 'Mr [Joshua] Reynolds seldom succeeds with women, Mr Ramsay is formed to paint them,' was the opinion of writer and art historian Horace Walpole. A pupil of Reynolds, James Northcote, is recorded as saying of the portrait (not without a barb at Ramsay): 'She had a fan in her hand; Lord how she held that fan! It was weak in execution and ordinary in features, but the farthest possible from anything like vulgarity.'

It is also part of the story of how a German princely family (and the Queen, an immigrant in Georgian England), reinvented itself as quintessentially British. The book under her elbow is a history of Britain, and there are unmistakable echoes of George III's famous words in his accession speech to Parliament: 'Born and educated in this country, I glory in the name of Britain.'

But interest in this German-born Queen recently reached fever pitch with Netflix's Bridgerton, in which she is portrayed with the perfect amount of aristocratic charm and general disdain by Guyanese-British actor Golda Rosheuvel. Can this portrait help uncover the mystery of whether she was the first black queen in the UK?

A theory first advanced by the Jamaican-American author J. A. Rogers in 1940 suggests that Queen Charlotte's distant ancestry through the Portuguese royal dynasty included black Africans. Does 'ordinary in features' convey more? Is this veiled, arguably subconscious, racial prejudice? 'The nostrils spreading too wide; the mouth has the same fault,' was Horace Walpole's sneering assessment of the queen when he first saw her. But the same Walpole stressed how pale she was, and his overall description was not unfriendly.

Ramsay's portraits, known for their fidelity to the original, are at the centre of this debate. You can form your own opinion, but it is not difficult to see how Rogers could know 'a little [black] musician, whose features, especially the mouth, is strikingly like hers'. And whatever Walpole's impression and the truth of her ancestry, Queen Charlotte definitely does not look pale in Ramsay's portrait.

Georgy Kantor, Keeper of College Pictures, St John's College, Oxford

A version of this article was originally published by The Guardian as part of The Great British Art Tour