Okay, for those that don't know their Chinese Mythology:
There are four gods of the seasons. Suzaku is the fiery Phoenix of the Summer, God of the South, represented by red. Byakko the White is the God of the West and Autumn. Seiryu, or Qin Long, is the Blue-Green Dragon of the East and the God of Spring. And Lastly is Genbu the Black, God of the North and Winter.
That said, it's safe to assume this is how the emperors work. Red-haired Shanks, Whitebeard, Blue-green "___" and Black "".
Now, let's focus in on one of those. The Blue-green. Notice any particular One Piece character that has Blue-green going on? That's right, none other than Buggy the Clown. Now, we all know that Buggy is not one of the 4 emperors (It's laughable to think so), but look at one of the men that Monkey D. Garp reveals to us. Looks like a clown, doesn't he? Perhaps Buggy's father?
It would make a lot of sense. Buggy grew up training with Shanks, one of the Emperors, he has met Whitebeard, and he has been to the Grand Line before. more than likely, Buggy's father could have introduced Buggy at a young age to the strongest man in the world, putting things in perspective for him. That would explain why Buggy is deathly afraid of Whitebeard, and also why Shanks and he would know each other and yet be on vastly different levels.
With that said, we could expect more of Buggy once we meet up with his father. Clown family reunion = good times, eh?