Daniel, I suppose the first question is “why does it need to be red?” Anything that animates is going to catch the user’s attention anyway, so I don’t see any great harm in keying the background to the theme.
That said, since gtk+ 2.10, haven’t themes been able to support additional named colours, to highlight things like ‘errors’ and ‘warnings’ where appropriate? So shouldn’t Clearlooks and the other themes be providing these now? Or did we just never decide what the standard list of named colours should be? :/