It's short for Roy-gee-biv. Because he's a rainbow.

[She's had to explain this way too often lately; it's starting to lose its punch for her. Tess makes an annoyed sound in her throat; it seems today is the day for secrets to come out. Cool, that's fine. She didn't even like those secrets anyway.]

Yeah, that'd probably be a problem if it weren't for the fact that I can talk to him.