Thunderbird

I personally theorize that Gallus is part Hippogriff. He’s the only pastel colored griffon in the show, the only other species like griffons with that trait being the hippogriffs, and not only that, but he doesn’t have the neck plumage every other griffon, young or old, all have. He also has two types of head feathers. The kind like Gilda’s and the kind that look kinda like ears, which is typically seen on the hippogriffs. If he is, in fact, part hippogriff, then that would explain his coloration and his status as an outcast in Griffonstone since the griffons are generally proud of their lineage. Anything other than pure griffon blood would likely be looked down upon. His being an orphan could be caused by his parents being chased out (or some other terrible fate, which seems to be more likely since Gallus isn’t with them) by the rest of the griffons. I didn’t list all the similarities Gallus shares with the hippogriffs, but if you compare and contrast Gilda, Gallus, and Terramar below, you can probably find more than what I listed.