A insult used to offend somebody who goes against a dedicated cause they used to stand by. It's origin comes from the anime Code Geass when one of the antagonists is accused of treason when the main protagonist uses a bluff to cause suspicion on the antagonist.
(person1 and person2 talking about person3)
person1: He says he's a faithful lover yet he always cheats on his girlfriend!
person2: Yeah he's obviously an orange boy.
A boy who is fairly orange in color.
Kristie "hey, did you see that orange boy?"
Girl "Yea, matts over there."