This sounds exactly like the problem I am having with my Core2 MacBook Pro, but applied to a different scenario. I simply cannot get consistent colour when outputting to the web - it is correct in unmanaged applications, but as soon as colour management kicks in, the colours are wrong.
I actually suspect that something to do with ColorSync is broken on Intel macs, as I have tried everything I can think of to try and get it sorted, and as far as I can see, I haven't made any mistakes creating/setting up profiles etc.