Keep them in the QT for at least two weeks. Longer if the mystery white spots are still there. Watch them for bacterial infections.

I photoshopped that picture... seems like it should be okay. The spots are not raised, or otherwise disfigured. It is, as you said, as if it is just pigment loss there. Maybe they are just coloring up...and doing so in patches? Dunno... but it doesn't look fungal to me.

D