Teddy would even make his hair look black/dark green in the beginning, so yeah, that was probably the in-universe reason. Off-universe, Allan Heinberg probably just didn’t wanna reveal much about the character early on.
You know, the way Marvel is promoting the upcoming Children Of The Atom book actually reminds me a lot of the Young Avengers in the beginning. I wonder how much they’ll end up resembling the YA, in terms of breaking expectations and character development.