If someone renames and they are on your friend list (or foe list) and you're online, you'll see them with normal average user colour, until you relog. However, if you foed them (if they were friended) or friend them (if they were foed) and then you relog, then they are stuck in a state of friend/foe and you can't remove them from either category. They then quack in blue.
I am fairly certain it can be fixed by simply reversing the progress (i.e when the person renames, you can foe them and unfoe them, and then when you relog they will not longer be foed).