I dunno Bejay, is there any way for you to post a picture?

Most of us evolve to growing at least some heirloom and open pollinated tomatoes, somewhere along the way. I have found them to be generally less productive and more disease prone than my favorite hybrids. I consider that as just a part of the price that I am willing to pay to have the diversity of the different colors, shapes and flavors of the heirlooms.

That may be contrary to what some maintain, but it is what happens in my garden in my little corner of the world. I also found that they are usually quite a bit improved in the second and third years, being grown from seed that I saved. Some contend that that does not happen, but it did for me. I do not think that they evolved or mutated that fast, just had a chance to more nearly live up to their potential in my location, soil and climate.

What variety are you having problems with? Could it be purple instead of black? Cold temperatures on seedlings can inhibit taking up one of the P elements (Phosphorus I think) which causes the stems and veins, particularly on the underside of the leaves to turn purple). If that is the problem, go ahead and transplant them into the garden and as soon as the weather is warm enough in your area, they will recover, get on past it and do just fine.
I don't know if this helps any at all or not, but hope so.
Bill P.