Vapor trails do not make rainbows. I have seen fresh contrails from 30kft that had strange condensation patterns and spectral refraction. I don't know about intentional spraying, except it must be happening in places, based on the myriad of weather control patents, but there is alumina and barium based antirust and antifreeze additives, respectively, and these cause chemically and visibly different trails. not only that but the particulates that fall out to the ground have been measured in many places, places otherwise far from industries, but under major flight paths.