I've just had a look at a Corsair article in Scale Aviation Modeller international. There is no indication of "formation lights", however this is an article on FAA and Commonwealth Corsairs. Looking at the instructions in my Tamiya F4U-1D they show what I think are the lights you refer to. They are on top of the wing, some way in from the end and near the aileron hinge line. The instructions give these as X-4 which is blue, the nav lights are, as Martin says Green and Red. If your model is a F4U-D then blue could be the answer. Personally I still have my doubts, because starboard nav lights could be blue or green, so there could still be a potential problem, if flying with other aircraft (that have a blue starboard nav light). Unless of course they are strobes, as I think modern planes have?
It's just a couple of lights

It's this sort of frustrating detail that gets me pinned down, If you do find the difinative answer I would be very interested
Mal