How about a blue assessor, Assessor macneilli? They're mild mannered but may also be a problem around shrimp perhaps...I'll look into it and get back with ya. The only problem is that they're hard to come by. One LFS near me had them pretty often for a few months and I haven't seen them since. Perhaps it's something that they can special order for you, or perhaps SWF can get one for you if you email them?
Also, how about a flameback angelfish, Centropyge aurantonotus or perhaps a cherub angelfish argi? I wouldn't classify any angelfish as a species reef safe because, although many aquarists own them without problems, some individuals can be destructive. That said, I think that these two species are some of the better angel choices for reefs that match your blue requirement...the size is right too.