I wouldn't give up on those seedlings. They do not look that bad, and you say you only have 4 weeks left....so hold tight to them:) Now onto your issues...the purpling color could be coming from temperatures. Not sure what they are experiencing, but once you'll get them out they'll be fine....and I don't see that much purple on your pictures. Your watering regime seems fine...just make sure the cups are light feeling, and that you aren't going by what the surface looks like....that could be very deceiving and cause some issues with cold/wet, then that causing the purpling. We fertilize our seedlings minimally...only with fish emulsion....we don't want them going crazy in their temporary homes....and we don't want them giving oodles of vegetative growth. You might be seeing a nutrient overload happening...esp. with the 10-10-10 applications. And finally, some varities have very, very wispy foliage. I am not familiar with those you are growing....but alot of paste tomatoes have droopy foliage....somewhat like they would be lacking water. Hope this helps... m

My four cherokee purple plants came from tomatoes I grew last summer, that came from a tomato I ate in NC the summer before. Last year I had a huge yield from 4 plants. This year, all 4 plants have been stricken with leaves curling up, new and larger leaves. Leathery, really curly little leaves and curled (up) larger leaves. Some small brown spots on larger, older leaves, no yellowing, no dead edges. Growing conditions are ditto to last year. Plants leaves are stunted, growth is stunted. You can see through the plants and overall, the leaves are small yep, and curled. I was told to use Happy Frog fertilizer due to calcium shortage. I don't think this will work. I am going to spray for fungus AND insects. These tomatoes are the best I ever ate, and I've eaten a lot of them. No more seeds available. I should have saved a few.

Bad news coming. Really nice pictures of herbicide (weed killer) damage. If you or someone else didn't use herbicide, possibly contaminated compost or manure. Similar damage on potato could occur with either scenario. RE the contaminated compost or mulch, see this from WSU: http://www.puyallup.wsu.edu/soilmgmt/Clopyralid.htm If you think that might be possible, be certain to run the simple bio-assay described at the above site. Here is a link that might be useful: herbicide contaminated OM

linchat I think it must be a bacterial or fungal infection of some sort, and you can't treat it until you know what it is. South Florida humidity and insect paradise is a great breeding ground for tomato diseases! Contact your state or county extension agent and ask what kind of pictures you need to send so they can make at least a tentative ID of one or more possibilities. Also keep Bets's advice in mind. While I don't think underwatering would make leaves "mushy" or gummy but rather all dried out, make sure it has sufficient water. It doesn't look like the plant is ready to expire yet so it's good to think ahead. And one more thing. The containers. Are they black? The heat of the sun beating on black containers can cook your roots and kill your plants presto. If they were my plants, I'd transfer them to a container that's light-colored, that won't absorb the sun's heat. Or at the very least, shade the containers in some way.