Purple leaves/stems usually indicates that they have been growing in a cool place. They will be absolutely fine when things warm up :).

I wish I could say that is so, but it has been 70-80 degrees outside with temps rarely hitting below 50 at night time all week long. I keep them outside during the day and on heating pads inside during the night. This is something I recently noticed so I think it likely just developed. The purpling is mainly on the new growth I noticed.

I don't see the purple in the picture, but it's possibly phosphorus deficiency, then, except it should be on the old growth instead. Phosphorus is very important when it's cold, but deficiency can happen when it's warm, too.

What variety is it? Some are supposed to be purple.

Yeah, phosphorous, but the plants are still very small, their roots not fully established, it's sometimes unavoidable.

Ok Thank you. I still have about 18 days before I planned to put my tomatos outside so they have a few more weeks of growing to do. I know its hard to see in the photo but the bottom photo, the leaf next to my thumb, that is not a shadow that is purpling from the underside of the leaf and the veins are dark but it was next to impossible to get a photo for some reason. They are Roma tomatoes. So just let it be until I transplant and then fertilize? which was gonna do anyhow.

I've never used heat mats but from what I've read, you shouldn't be using them after germination anyway.

Just to update- the tomato plant that had significant purpling under the leaves, and still does, is very far behind in growth compared to another tomato plant i germinated at the same exact time under the same exact conditions. Im not sure why and Im still hoping it grows out of it. Top pic is obviously the larger plant while the bottom one has just stopped moving.

It's totally common for young tomatoes to have a purplish tinge. Is it a phosphorus deficiency? Probably yes, technically, in the plant, but it's usually a result of an immature root system or stressed root system due to conditions that are hard to avoid in starter pots/cells, etc., so unless there are other signs of nutrient deficiency, IMO it's something that's best ignored rather than risking damage potentially overfertilizing trying to correct it. I've never seen it permanently damage or stunt tomatoes, and they do very well and grow out of it once planted out into the ground/large outdoor container and the weather warms up.

I would have lightly fertilized the plant in the photo, as, even ignoring the purple, it looked pale and in need of some nutrients. AND I would have double-checked that the drainage holes were adequate.

If you planted it out and didn't fertilize at plant out, I'd give it a one-time shot of something with some nitrogen in it. Something like fish fertilizer, very diluted lawn fertilizer, Miracle Gro, etc. works well. Then, for the rest of the season, fertilize as normal with a tomato-appropriate fertilizer.

Thanks again Gorbelly! You are always so helpful ^.^ I ended up clipping off the lowest leaves of the plant, adding in more soil and garden soil and burying the stem deeper into soil. Then I watered it with a very diluted solution of Miracle gro tomato fertilizer. It is about a day or two later and the plant has started growing again! I think I was messing with these two plants a bit too much, as far as transplanting and watering, things like that so they had a harder time. I have two othertomato plants i germinated about 3 weeks apart and they seem to be doing much better than my first two. Im finding that when it comes to gardening, less is more. First year ya, so you live and learn.