Hmmm, my post disappeared!
Whatever it is, it seems to be gone. I think what the poster thought was aphids was just residue dust from transplanting. No way are they aphids - I would be deluging the plants in insecticide if they were. They nearly wiped out my first seedlings. Whatever this stuff is, the plants don't seem to suffer.
I may be leaning toward the idea of it being due to flaking of the lights, as the plants not under lights - four peppers and four tomatoes do not have any white stuff on them and the ones in the back two rows had very little. But the front light is old, someone read an article about me trying to buy lights in a store and acccusing me of growing the "other" type of plants, so he gave me the light. I've also been using a fan for a little longer each day which may be helping.
Mike