Residing in the Ambassador's Room, the painting shows two young ladies dressed in the finery of the day, each looking every inch the aristocrat. But one of the women is black, and this was 1779, a time when the grotesque business of slavery was booming and inequality was written into law. From this one painting, myriad questions arise.
The British director Amma Asante knows the power of that painting, even in postcard form. When the image dropped through Asante's door, attached to a script by Misan Sagay, it demanded to be noticed.
"I just knew this was unusual, different, it gave me a funny feeling and was unlike anything I had ever seen," says Asante.
The black woman in the painting was Dido Elizabeth Belle, and her story is set out in Belle, a new film out next week. To coincide with the release, Scone Palace is staging a special exhibition on Belle, and Perth Playhouse hosts the Scottish premiere on June 12.
Belle was the illegitimate daughter of an African woman and a British naval officer. When Belle's mother died, her father asked his uncle to take the child in. The uncle was none other than Lord Mansfield, the Scots-born Lord Chief Justice of England and Wales, and a man who was to play a pivotal role in the fight between abolitionists and slave traders.
Asante, 45, who may be recognisable to readers of a certain age from her Grange Hill days (she played Cheryl Webb in the famous Zammo/heroin storyline), made her directorial mark in 2004 with A Way Of Life, a Bafta-winning drama about racism. Although Belle is a period piece, complete with all the carriage and bonnet trappings, Asante was determined it should have something new to say. "What was its value today, why did it resonate today, why tell this story to contemporary audiences now?"
Her answer was that many of the questions Belle faces about identity are still as relevant. "It is really important we know our history in terms of the difficulties we had to overcome." Moreover, this was a story about standing up to injustice. "We need to harness the great things that have happened in our history, what happens when ordinary people fight against their conditioning to do good things, to do the right thing, what courage can do when we harness it."
Belle is played by Gugu Mbatha-Raw, who describes Asante as "a force of nature". She is a thoroughly nice force of nature, one who still remembers The Herald ran a piece on A Way Of Life 10 years ago, and thanks us again for it. She is also a force of nature who is about to break very big. On the strength of Belle she has already been named as the director of a new Hollywood thriller, Unforgettable. Not bad for a "painfully shy" kid from Streatham, London.
Her accountant father, who died during the making of Belle, had an unusual idea about how to cure that shyness - stage school. This was the Fame era, when to be at a drama school was some children's idea of heaven. Not for Asante. At least not at first.
"I went to the school for my interview and it terrified me. There were all these kids in leotards, leaping around and a huge stage in the assembly room. I thought my dad was punishing me. I just didn't know how it would ever work for me. It was far away from home, one and a half hours away. It was quite traumatic."
What she got from the school, then and now, was a sense that competition could be a good thing, that it could inspire someone, no matter how shy, to take chances.
"That has instilled in me a kind of backbone when it comes to being in a minority as a female director, as a female who tells stories, because I just think, 'Yes well life's hard, it is going to be hard, and you've just got to get on with it'."
By the end of 18 months, she realised dad had been right. "I really loved it. But I was not a good actress," she says, with a laugh. Still, she landed a part in Grange Hill, the hugely popular school drama that was the Coronation Street of its day for the under-16 set.
"Once again it was another leap, it was these kids who had been working on TV for years, some of them were already 17 and had driving licences and big flash cars. Everybody seemed like a child who was an adult."
The anti-drugs storyline led to an invitation to fly to Washington DC from First Lady Nancy Reagan, who was fronting a "Just Say No" campaign at the time. Asante was the first in her family to go to America, never mind receive an invitation to the White House. All she and her fellow actors could think of, however, was getting hold of some toilet paper. They were convinced it would be something silky and radically different to the stuff used at home, she says. Alas, it was not.
After leaving school, Asante found there were few to no parts for black actresses, so she took a typing course. As a way to build her speed, she wrote a story and typed it out over and over. Eventually, one of her tales landed in the hands of a producer and she began writing for television. That, in turn, led to the chance to direct A Way Of Life. But as so many other directors have found, that all-important second feature remained elusive.
"What I had was a lot of people saying we love your work, we want to work with you, but not on this story. Whatever story I brought to them it was never that story." When three movies collapsed she thought maybe it was not going to happen for her. A break, a new marriage (her first husband was a producer), a new country (she moved to Holland) left her ready for the fray again. Then a postcard dropped through the door.
Although success has arrived for her, she does not forget the slog along the way, and she has been among those who have lobbied the Government for more opportunities for black filmmakers. Mentoring and training is great, she says, but it is getting on in the business that counts.
"If you are going to put your money where your mouth is, it is not just about (saying) look how many schemes we've got and how many opportunities we have for people coming in. Why do they never get past a certain point? Why are they never the people who are commissioning? Why are they never the people who are producing or directing?
"It's not just for the good of women, or just for the good of people of colour. It's for the good of the industry."
Belle opens in cinemas on June 13. An exhibition, Dido Belle - Her Story, runs at Scone Palace until October 31.