Rainbow Boy is quite the interesting character.
His name and the fact that his power is "the brilliance of [his] rainbow..." all point to one thing. He's got to be gay.
I've known quite a few gay men who seem to have that power.
The problem is that rainbows didn't become "gay" until around 1978, and Rainbow Boy debuted in 1942. So the whole rainbow motif doesn't really support any conjecture on that part.
What does make a case for his fairy-ness is that fact that every time he enters a room, he comes flitting in like he's doing some ballet:
One the other hand: Rainbow Boy is a DICK!
In the story I ran a few weeks back, Rainbow Boy helps save the earth from invasion by kidnapping the alien general and taking him around to show how being a dictator is a bad thing. Here's a look at the horrors they encountered:
Now the problem with this is... Rainbow Boy let all those people DIE!
Yes, he is trying to prove a point, but couldn't he have proven it by "Look at what they're about to do...now excuse me while I go rescue those people!" But he makes no attempt. I'm surprised he didn't bring along popcorn for the show.
And he's practically smiling in panel four when he says, "I'm going to show you more!" With an explanation point...
Yippee! Let's go!!
Rainbow Boy is a bad bad person. He may have saved the world from an alien attack, but my conclusion is he's still to evil too be gay.
That's my story and I'm sticking to it.