One of the best places to study horse color is the wash rack, and BreyerFest was no exception. This is one of the guest horses at the event, Pecos. He is a 13 year-old PRE stallion. As the pictures in the link show, he appears to be a grey that has turned uniformly white. When wet, though, small spots of depigmented skin are visible.
Many greys lose pigment as they age, and this seems particularly true of horses of Spanish descent. What makes the depigmentation on Pecos a bit unusual is that it is not concentrated on his face or his undersides. Notice in the picture above that his sheath area is still quite dark. (I did not think to take a shot of the area under his tail, unfortunately, but I suspect it too is still mostly dark.)
This shot shows that his face is also mostly dark.
I did not get any shots of the front of his nose since he was rather intent upon wuffling the rack, but this picture shows how the area around the borders of his marking as started to mottle. That is common in older greys and seems especially common in the breeds that are prone to depigmentation.
Two of the breeds covered in the upcoming book – the Boulonnais and the Kladruber – get an even more dramatic form of pigment loss that appears to effect the face. Studies done in the Czech Republic suggested that the two types of depigmentation in greys – one concentrated on the undersides and one on the face – are genetically distinct from one another.
Neither look much like what is going on with Pecos. His owner said that this was a recent development and that they thought it was a reaction to medication.
The spots are also unlike Tetrarch spots, named for the famous grey racehorse who had them.
Tetrarch spots usually appear in the earlier stages of greying, and disappear as the horse greys out. Photos suggest that these kinds of spots have dark skin under the white hair, rather than white skin like the spots on Pecos.
Pictures of one of the extensively depigmented Kladrubers appear in the upcoming book. Horses like that are interesting because their presence could mask others kinds of patterning in an all-grey (or mostly grey) breed.