In this case, I'd stick to the Red State, Blue State for the speech bubbles. The ale&wenches for captions could work well, but I'm afraid I can't judge from my imagination only. It's my experience form other medias, mainly fanfictoin or generally writing, that screenreaders tend to be hasty consumers who want to have it easy. And it's certainly wise to take the reflections you mention into consideration for the webcomic.