Sorry, says we must log in.

Unlikely to be virus.

Purpling is commonly due to little or no fertilizer, and/or cool temps, especially in the root zone.

So strange. I have my photos set to be viewable by everyone...

Anyway, turned out to be nutrient deficiency. After repotting them into a mix of peat/compost/garden soil, they have begun growing vigorously again with a marked lessening of the purple under the leaves.

Thanks for the help.

My baby tomatoes look just like yours. On a different thread, it was suggested that it could be too much watering, or even too much feeding. When I potted them up, I just put them in seed-starting mix and I'm thinking that was the problem -- not enough nutrients! You're saying that you solved the problem just re-potting in new soil. You didn't feed them at all? What kind of compost did you use?

Here is a link that might be useful: My Blog!