Friend or foe. This is especially important in unclaimed space where a supposed 'friendly' target can be hostile, without changing their colors.

This closely ties in with another thread in bugs:

http://www.vendetta-online.com/x/msgboard/2/5772#74112

Maybe there should also be another status between friend and foe - so someone with ambiguous ratings would show up a different color, gray or white maybe.

Also, other games (Descent Freespace for instance) have friendly targets turn hostile as soon as you or they do something hostile, like shoot a friendly.