So basically if one of them are grey, they are dead in the underworld(where they are right now), if they're blue, that means that dead bats can see a blue shine if an alive bat comes down into the underworld. Goth bit Griffin and took his life, so Shade gave Griffin his life, because Griffin is Shade's son. Whats so sad is when he was rescuing him, that was the first, and last, time Shade had even SEEN his son