already wrote about this two weeks ago.
the client wil handle it this way:
1. check if address is within own address book -> green
2. if account exist within blockchain -> yellow
3. don't exist within blockchain -> red
simple visual control.
Why invent crazy schemes when there is a simple, elegant solution, which covers both client AND server - checksums. The way it's implemented in bitcoin.
I don't buy the whole "oh my god performance" line of reasoning. You wrote it in Java, for god's sake
