A green with a small g is someone who is environmentally friendly or concerned about the environment. An environmentalist. Green with a capital G though refers to a member of a Green party. According to Wikipedia
Either type of green/Green is welcome on this site, so long as they’re also a geek. Again, according to Wikipedia, a geek is
though it says there’s also the pejorative meaning of
peculiar or otherwise dislikable person, esp[ecially] one who is perceived to be overly intellectual
I don’t think there’s anything wrong with being peculiar and it’s not possible to be overly intellectual, and worrying about whether or not people like you is very ungeeky.