Dapple grey was my favourite horse colour all through childhood. It's also one I really struggle to paint, so good references are a must!
Ex-racehorse (Bakewell Show, 2014):
Hunter classes (various):
One gorgeous hunter in particular (Ashover Show 2013):
Heavy horses (Hillside Animal Rescue, 2014):
Genetics of grey horses: According to the wonder book grey horses all have an underlying "other colour", but fade to white over time. They retain their black skin so are never truly "white" - the trick question asked of most little kids the first time they ride a grey pony! Each time grey horses moult they get lighter, some going dappled, fleabitten or iron grey along the way.
If you would like to use these photos as model painting references please go ahead, I only ask that you share a link to the blog if you put your work online. Of course, if the photos of your horse and you would like them removing, I will do - or feel free to use them yourself. Thank you!