A list of horse coat colours taken from The School of Horsemanship by François Robichon de la Guérinière (first complete edition 1733. Translated by Tracey Boucher. Published by J A Allen, London, 1994):
tiger (grey with black spots and large solid black areas on white undercoat)
pied (black, bay, chestnut)
moor’s head roan (blue roan)
wolf-coloured (with dorsal stripe)
all-flower or peach blossom
trout (a black undercoat and a body and head dotted with reddish or chestnut spots)
blue-grey (“a white undercoat and spots over the entire body, such as one sees on porcelain vases”)
UPDATE 17/1/2017: I rediscovered my copy of The Wilton House Riding School, a reproduction of 55 paintings by Hapsburg riding master Baron Reis d’Eisenberg depicting haute-école movements. I can’t find a date for the completion of the paintings but in his introduction Dorian Williams says that the baron lived in the mid-eighteenth century. As I flipped through the pages I noticed that several of the colours mentioned by Guerinière appear, which might help to decipher the original French list.
There’s a German-bred horse described as a “porcelain piebald” which turns out to be a dapple grey (he’s called “Superb”). A Turkish horse is “silver trout” – what we would call flea-bitten grey. A leopard-spotted appaloosa is “tiger” (a confusion I’ve come across in some nineteenth-century descriptions of spotted horses). Our mysterious “mille fleurs” or all-flower looks rather like a blue roan with black freckles.