As you can see by the map below, France is a predominantly brown haired country. This makes anyone who is a natural blonde stand out, and I've always thought that one of the reasons Agnes Sorel made such an impact on King Charles VII is that she was a natural blue eyed blonde, in a court full of dark haired women. They met in 1443 when she was a young woman of around 20. He had been on the throne all her life and was around 40 when they met. She became his mistress soon after.
Her family came from Picardy (in the light haired zone), where they were minor but long established nobility. As a teenager she joined the household of the Duke and Duchess of Anjou (also known as the King of Naples and the Duchess of Lorraine). It was normal for young people to enter other households like this, with the parents hoping to forge stronger links with important patrons. They would receive an allowance, in return for agreed services, suitable for their rank and age. As well, these children would be educated and groomed for roles at court and marriages would be negotiated. Agnes's father must have been very well liked or respected, as the household Agnes entered was second only to the immediate Royal Family. Indeed, the Duke was the King's brother in law, and personally close to him. Agnes ended up exceptionally well educated, as this was a cultured and sophisticated household. She was clearly a clever child and soaked it all up.
As a young woman she became known as la Dame de Beauté, known for her great physical beauty, her lavish lifestyle and her influence on fashionable dress. As one of the King's closest confidents, she had political and social influence, often behind the scenes but there were occasions when the King nominated her as his agent. No other mistress had been so publically acknowledged. Like many women with both beauty and brains, she tended to polarise those around her, and she made powerful friends, but equally powerful enemies.
This painting by Jehan Fouquet is accepted as being an image of the Virgin, using the features of Agnes Sorel. Commissioned by Etienne Chevalier, the King's secretary, this was a common way of flattering an important ally.
We know from contemporary records and paintings that she was blonde, and her physical remains, examined in 2005, bear this out. Her long golden locks are discreetly portrayed in the famous painting by Jehan Fouquet on the right hand side of the Melun Diptych. You can see them streaming down the back of her neck and tightly pulled back at her temples.