I'm by no means an expert, but I remembered reading about discolorations in a book I just got on Terrace (Balcony) Gardening so I looked it up. Sorry-not much on curling that I could recall or find.
The three types of discoloration listed are yellowing between veins, general poor health and new leaves misshapen/discolored. I can't tell from the photo which might be more likely so I'll give what it says on each.
For yellow between veins, she mentions the cause could be mineral or trace element deficiency, or insufficient oxygen around roots. Solutions would be to add fertilizer or organic material, and to lighten the soil mix for better air circulation.
The only cause listed for general poor health is malnutrition, thus the solution would be fertilizer or fresh organic metter.
She lists three causes for new leaf deformations or discolorations. The first is malnutrition, the second is poor light and the third is viruses. The first two have obvious solutions. For viral issues in tomatoes the solution is probably more harmful than the problem, so I'd either let them be or throw them out and try again.

FYI The book I'm pulling all this from is The Terrace Gardener's Handbook by Linda Yang.

Nitrogen deficiency

Growth dwarfed, thin and upright habit; stem and petioles rigid; leaves pale green, occasional purplish tints, older leaves yellowing.

I would fertilize a bit more and stay on top of the watering. Looks like pretty course soil so it drains and dries out fast.

Damon

Thanks. I'm going to up the fertilizer and water. It has been warm, sunny, and dry for the last few weeks. Luxurious problems!! Now that the plants are getting some size, they drink a lot and the medium is very fast draining. I'm not too worried, they are growing well, and have lots of blossoms. I've never over fertilized a plant "yet." My only 5 gal SWC has a full cup of fertilizer around the top rim, and that plant looks really good.