Lady Cas has a Tiger

"The ladies & dandies have taken to ride in the Mall in St James’s Park in such numbers as to be quite a nuisance."

'To me it appears quite as strange to meet with people who have no ear for music, and cannot distinguish one air from another, as to meet with people who are dumb. [….] There are people who have no idea for difference of colour. The Duke of Marlborough cannot actually tell scarlet from green!'

King George III (quoted in George III by Christopher Hibbert) 

This is one of the earliest mentions I have yet encountered regarding what is apparently red-green colorblindness. The first scientific paper published on the subject was by John Dalton (1766-1844) in 1798, ‘Extraordinary Facts relating to the vision of colours,’ which he presented to the Manchester Literary and Philosophical Society. Dalton and his brother were both colorblind, leading to his interest in the subject, but before his paper there was precious little awareness that some people possessed limited color perception, although famous scientists like Robert Boyle and Isaac Newton had previously commented on their apparent insufficiency in discerning color. 

Though his theory that discoloration of the vitreous humour, the liquid inside the eyeball, was responsible is incorrect (it is actually an absence of red-green photoreceptors), he recognized both its hereditary and sex-linked nature; the condition officially termed deuteranopia or deuteroanolomy (depending on whether the photoreceptors are missing or simply mutated) is sometimes called Daltonism in various languages his honor. 

'How unfortunate for true virtuousi that such an eye should possess objects worthy of the most discerning — the treasures of Blenheim!' 

Fanny Burney, on Marlborough’s color-blindness

Unsurprisingly, people with color-blindness were often derided (or lamented, depending on their status) as being rather coarse or provincial, unable to discern the subtle differences between a Lawrence and a Gainsborough or enjoy the “painted music of a Turner” (x).