Faye I am with you. I scratch my head every time I see a coloured TB, because both the Australian studbook and the English one have no cream. I just can't compute a pally lol.
I think there must have been a time in the US when their books weren't as closed as they are now. Either that, or way back in yesteryear, a cream boy jumped a fence and fell in love with a beautiful TB lady
Thoroughbreds carry, albeit very rarely, the cream, rabicano, sabino, and overo genes. Much more common now that people are breeding for their color. There are quite a few dilute stallions standing in the united states and a few in Australia. It was actually introduced a long time ago, and while the gene does not exist in arabians, it was probably introduced by the same ancesters of modern Akhal Tekes. Many buckskins where registered as "duns", which doesn't exist in modern thoroughbreds or as simply "chestnuts" or "bays"
All Dilutes today can be traced back to two stallion's Milkie (registered as a chestnut, but clearly a palomino) and Glitter Please (registered as a bay, but clearly a buckskin), although clearly their are more incorrectly registered in their lines.
I can think of quite a few dilute stallions off the top of my head, Guaranteed Gold (cremello), Issues of Gold (palomino), Zillionaire (cremello), Pure White Gold (genetically a palomino Overo, but he's white), Sato (sabino palomino thoroughbred), and Milkie's Desire (palomino).