well.
guentheri and xanthurus has a overall, similar colouration. white with orange-yellow posterior.
so the two when mixed, doesn't give a very blarring obvious sign.
we identify one of the parent first.
look at the forehead. there is a small crown. this crown came from the xanthurus. however, the crown is not as strong as a full blood xanthurus because it has been diluted by the crownless guentheri.
look at the body markings too. it has a slightly criss-crossed marking, similar to xanthurus. xanthurus has a very strong chevron mark. but this hybrid is more spotty, but the chevron pattern is still obvious.
now for parent 2.
the dorsal fin is a little yellowish, compared to pure white for xanthurus. the guentheri blood gave it the yellowish tint. also. guentheri has spots on the body which, when mixed with the chevron from xanthurus, gave a chevron-spotty design.
often times it's very difficult to guess the hybrid. so just look at the overall appearance and try to match which parent gave which design.
it's like putting a whole poster of butterflies and try matching them to see if they give you something that looks like the hybrid.
also take into consideration the range in which they overlap.
for example, a spotfin butterfly will never hybridise with a raccoon butterfly.
hope that helps. but most of the time, it's still a guessing game.