Looks like aphids.

Have the nights been particularly cool? That might explain the purplish color.

Anyhow, fertilize with an all-purpose fertilizer that contains micronutrients as well as the standard issue npk.

Thanks for the reply, lionheart!

I didn't know that cool nights could cause the purpling - how does that happen I wonder - less available phosphorous? This last week has been very warm, but about a week or so ago we did have some cool nights.

I did apply Tomato Tone recently. I wonder how long it should take to see improvements? The ones in the ground definitely look better than the ones in the pots, so I was attributing it to running out of nutrients and needing to get planted (before I saw the bugs and noticed the number of curling leaves and panic set in.) ;-)

Could overwatering be an issue? I've been so paranoid about them wilting in the sudden hot weather the last few days, I might be overdoing it.

Yeah, overwatering can cause problems. Usually it causes yellowing and wilting/curling, and it *might* be playing a part in the curling.

It's been suddenly hot here too, and by the end of the week it will be back to normal, which could mean cooler nights again. Anyhow, for watering requirements, stick your finger in the soil up to the second knuckle; if it's damp there's no need to water. But I know what you mean about the sudden explosion of heat. It can be tempting to overwater. :-)

My experience in my zone is that chilly days and nights (usually nights) can cause purpling. My understanding is that tomatoes cannot take up phosphorous when it gets too cold. They should gradually turn back to green but, if you get another cold snap and they get chilled again, they can pick up the purple coloring again.

The fact that they get purple for a while should not hurt them. You might want to spray fertilize (the foliage) with a seaweed or fish emulsion or another gentle fertilizer that contains P and other micronutrients, and that should help. That way, the plant can get what it needs through the leaves, instead of being completely dependent on the roots in cold soil. But, really, the purple will go away when the temps get consistently warmer, especially soil temps.

I think Tomato Tone may be a slow release fertilizer? It appears to be a very popular fertilizer and I have used it myself with no complaints and good results. But, since the purple indicates that the roots haven't gotten up to speed yet with taking in nutrients, do the foliage spray with a gentle fertilizer to green up the plants a bit quicker.

A lot of aphids can stress the plants a bit; a few usually aren't a significant problem. You can spray them off with a hose or use Neem oil. Be careful with Neem oil in the hot weather -- some people have reported leaf damage from Neem when the temps are high.

Your plants look otherwise healthy to me. Keep up the good work.

YOu asked "I didn't know that cool nights could cause the purpling - how does that happen I wonder - less available phosphorous? "

Not necessarily. Roots don't function well when it's cold. Thus, the plant is short of phosphorus.

Also, they're short of nitrogen -- the telltale symptom is the nicely green new growth, while the older leaves are moving toward a yellow-green. So either fertilize or get them in the ground.

Thanks for the info - this is really helpful! Thanks for the reassurance too - This is my third year starting my own plants and even though I think I do a better job each year, there is so much to learn!

I will do a fish emulsion foliar spray. I did a little alfalfa tea applied last night, that should help with the nitrogen as well, right?

My in ground plants are all doing well - I just want to give my potted plants enough nutrition to keep them healthy until I get a chance to give them away. I want my plants to look like they're worth planting! :)

You said "I will do a fish emulsion foliar spray."

Why not skip that a give a "real" dose of nitrogen? Dilute the fish according to directions and water the plants with the fert-enriched liquid.