Oh, what an interesting question! I think his nickname would definitely depend on who was speaking to him. In the case of people who respect him/worship him (if the world ever got back to that!) he might be called things like the Bountiful One, Guardian of the Crops, Lord of the Fields, the Blue-winged Guardian, this kind of vein of thinking.
For friends, they would probably relate either to his blue bird form or his peach colored haired. If they wanted to pick on him, they could call him birdman... but I imagine he'd get Peachy, Birdy, neither of which he would mind. He also wouldn't mind being called 'Wren', which is the type of bird he is!
However, Illran would definitely give him the most endearing nicknames. Illran usually gives bad nicknames to people, but Veras is definitely an exception. Things like 'Sunshine', 'my Everything', though I also imagine he would call Veras some more respectful nicknames to make him a little embarrassed.
Veras, to me, seems like the kind of character who probably wouldn't have a nickname he was particuarly attached to or used himself, but wouldn't at all mind being called different nicknames by different people. He would value it as a sign of friendship-he'd like it a lot!