I have been playing with an idea of having different IFF colors on a same team. So that you could highlight mission critical ships for example.. step above escort list in function. Wing Commander Saga could use such feature for setting capships IFF colors separate from fighters or BTRL to mark the civilian fleet with a single color, battlestarts on another to make the radar much, much more useful. Or like in normal FS 2 campaign you could mark critical ships with alternate color to make them stand out.
However using iff_defs.tbl for this atm is very useful as the ships which have different IFF colors still belong to separate teams. This causes problems for example with fred as it freaks out when ordeting ship to escort 'non-hostile' ship, but also as the friendly but not same iff ships do not follow 'normal rules'. On my tests escorting fighters sometimes attacked the ship they were supposed to escort, no traitor or friendly fire warnings were given nor did the 'non-hostile' ship care if you blew it away. Also missiles could be locked to the 'non-hostiles'.
So fooling around with current IFF defs table doesn't seem to help much here. So i originally though of if IFF color could be made sexp toggleable but after brief consultation this doesnt seem to be a good idea.. However.. would it be possible to expand iff_defs.tbl to accept sort of 'same team' flags or identifiers (sort of like inverse of what the current $Attacks: entry does). So that certain IFFs would actually function as a single 'IFF entity'.
Or even better to allow modders (and fredders) to define IFF relations even more closely.. so that if wanted it could be made even more complex so that you can choose what Team A can do to Team B, i.e Team A can order Team B but Team B can't order Team A etc. which would probably make fredders happy.