Developer @ appear.in here. For lack of better ways of communicating, at which page did you experience this? We tested it on our own devices but couldn't replicate.
http://appear.in - just tried on iPad and got the same dark gray page with absolutely nothing on it. Not running iOS 7 on either of the devices though, perhaps check that?
I realize Mobile Safari may not be a supported browser, but a graceful failure with some sort of explanation wouldn't hurt, would it?