White spots on tomato seedling leaves

Last Friday I bought three tomato seedlings from our local nursery. Two have slightly wilted leaves but I think they will perk up in a day or two. One is an heirloom, Brandywine. The third is also a Brandywine and has little white (not white and brown) spots on the leaves although it is growing well and has a firm stalk with otherwise healthy-looking leaves. I transplanted it yesterday into a large pot (for balcony growing) the pot being filled with a new bag of MiracleGro Potting Mix. I didn't notice any spots before transplanting it.

I don't think it is Septoria leaf spot because there doesn't seem to be any brown color around the white, but can't track down anything else that looks even close.

Where I live the outdoor planting season for tomatoes doesn't begin until Memorial Day, so all three seedlings are being raised indoors until then.

Any suggestions?