Indeed; no story is quite as fun without various shades of gray. I prefer to explore motivations, so gray works just fine for me.

You're right. No matter the goals or ideals, the antagonist is the person who stands against the character around whom the story revolves. Needless to say, if a character we'd previously identified as an "antagonist" actually became the focal point of the story, he or she would switch roles.

I think that's part of the fun of Prep--learning which characters we want to focus on, debating the pros and cons of changing the focus of the story. I know it's proving to be great fun for me.

I'm reasonably certain that the character my protagonist identifies as an enemy will simply end up being an easy target for his accusations, so in the overall scheme of things, he's not a true antagonist (more of a deuteragonist, if we're getting right down to it, since the story will [probably] focuses on both of them as they recognize the inequalities in their world and try to act to change them in their own ways), but "antagonist" is an easy enough label to pin on him for now.

Prep is helping me figure things out, but so many things are up in the air. Nothing's super-glued in place at the moment. I think that's part of the charm of it.