Well, I'm no pattern expert, but his base color isn't grulla. I believe it's a dark bay, due to the lighter brown coloring around his muzzle. Grulla is a black based dun, which I don't think your guy is at all mostly because I also see no classic dun factors, like leg barring.
Hard to tell because he's got his winter coat on but I wouldnt say he's a grulla. Most likely a bay judging by the brown on his nose & between his legs.
Other than that, i'm not too fluent with Appy patterns.
He could be a classic roan under that varnish. I don't think he is a blue roan, again, black is the base colour and that brown muzzle doesn't lead one to think black base. Maybe a bay base classic roan with varnish.
Varnish can and does uncover spots. I find new ones on my mare every year. He could of very well of have a small blanket, but with the varnishing that far advanced it is almost impossible to tell. You could, in the spring/summer, wash him and it will show under his coat any white areas. Those white areas would be what white he was born with. Varnish does not affect the skin color underneath, just the hair color.