Skip Martin Gay?

No he wasn't gay. He couldnt get enough sex with Mary sue. Lol what happend was he tried to deny the fact that all the things that turned people colors he possessed inside himself aswell. Remember the book burning scene when he told mary sue it would be better if she burned her book? When bud gave his monologue in court skip finally turned colored because he finally accepted all those things were in him and he couldnt deny it anymore. Love love love this movie.

It amazes me that after all these years, people still think that sex caused all the changes.

But he did see the red rose in the garden after he had sex with Mary Sue/Jennifer.

I think it's because he really didn't have a choice in the matter. Jennifer basically coerced him into sex. Everyone else pretty much discovered sex because of Skip telling them about it and so they voluntarily did it on their own.

Wildcattin'...Wildcattin'. Pow! I'm gonna go.

He does turn color - in the courtroom scene, when George and a handful of the galley change.

And, as someone else pointed out, it's not about having sex. I'm sure some people did turn color after sex, but George, for example, turns color in front of us, never having had sex. It's hard to say exactly what causes the "change", but it's more about allowing for things to happen in ways you didn't think possible, previously. David/Bud only changes when he hits a guy in defense of someone. George changes when he realizes that he wants his wife, not just wants her to fill the role of wife. Jennifer/Mary Sue changes from discovering a book she genuinely likes, realizing books aren't horrible things - and in turning down sex. Big Bob changes when it stops being about making/keeping things pleasant and becomes about his own anger.

The change is internal, not external. Many of the people may have turned color and still gone back to roughly the same lives they had, if that's what they chose. They don't necessarily have to change their lives; it's about changing their way of thinking. The change in people is about becoming aware that the world is more complex than they'd previously believed. The change in stuff is about the world responding to people becoming aware of that complexity (the tree bursting into flames is the best example).