Surfactant leaching
Paint contains many inert materials that help it spread smoothly such as surfactants. As the paint cures in cooler weather, the surfactants can ‘leach’ to the surface due to condensation. On darker colors these surfactants can look like a white or creamy film on the finish. On lighter colors the film can look brownish. In either case, washing down the surface usually corrects the problem and it rarely reoccurs.