I didn’t even realize the spots were blue!
Actually, I think the Jersey Giant hides the blue.
Leghorns don’t typically have the blue gene.
Have you got blue chicks before with that rooster, OP?
He is paint.
The Leghorn is dominant white while the the Jersey Giant is recessive white.
The recessive white hides, revealing the black underneath.
Dominant white is really only incompletely dominant.
Dominant white II plus black ii gives you paint Ii.
Handsome Jersey Giant, by the way.