>>536447413
Probably Blue since we don't know if Goku under Toriyama can use UI at will (probably can't), and Piccolo commented Gammas are around both Goku's and Vegeta's levels, so Goku likely doesn't have a form above Vegeta's Blue.

That claim is so weird though, because if it is to be believed, then Gohan's Ultimate is near Blue level, since he kept up with Gamma#1...