Flashing could be from anything. And since it's not constant, it simply could just be an itch. White spots aren't always an indicative sign sign to look for as body flukes can begin as small red "pimple like" growths that will wind up having small, thin, white "stringy like" lesions in the end. With that being said, there's really not enough info to go on here and I would suggest to watch them for a few more days. If you notice anything more, then post in the sick fish area with as much info as possible and we can take it from there.