Roxxy - Warrior (the black leopard horse you have pictures of), is not grey, nor does he have grey heritage. Warrior is a Friesian appaloosa cross (3/4 Friesian). He has the leopard gene, and therefore is loosing spots with age. He will likely be solid white in his 20s, but it is not a grey gene. You see his pink nose, he is actually going white, not grey.
The Friesian will end up grey (you don't get 'white' horses), his mum carried the 'grey' gene which then got passed onto him, each year he gets lighter and lighter, just like a grey horse would, but with him his spots get lighter and lighter and eventually it's highly likely his spots will disappear completely