Many times I have indeed seen what you describe, outside during daylight hours, with the naked eye specks not only white, but mostly rainbow seemingly sort of 'swimming' around like miniture metors on a pre-determined flight path. Interesting theory on the sunlight perhaps that could be true. I always sort of thought it as energy of some sort, but I could see where sunlight could create this. Interesting though, this is the first time I've ever told anybody about this, I just figured I'm weird- so what.