To me, this sort of damage looks like Roundup (Glyphosate) damage as it commonly causes bleaching out of the plant color near the stem. (See photo of a similar tomato leaf in attached link.) There's nothing you can do except leave them alone and let them heal. If they were going to die, they probably already would have. I got similar glyphosate damage in my garden about 3 weeks ago after the county sprayed for weeds along the road. Some plants died, but most survived. Before you say "I didn't use Round-up", let me add that it can drift through the air a considerable difference--easily up to a mile. Some herbicides volatilize and turn into a vapor and travel through the air as a vapor and then settle on plants causing damage. So, you can get herbicide damage even though you aren't using the herbicide yourself.

Here's the link that shows Glyphosate damage on a tomato plant:

Herbicide damage

If your plants were yellowing from waterlogged clay soil following heavy rainfall, the yellowing would be more widespread.

Hope this helps,

Dawn

Thank you, Dawn. That is a real possibility, as I did spot spray in the driveway near there with some weed killer a week or so ago. I thought I was careful, but like you say, it probably drifted. That is actually a relief, as I was afraid it was something more difficult to deal with..