Tomatoes are tropical -- they can take full sunlight anywhere. It could be lack of water but I doubt it. Plants with water deficiency wilt like crazy while they are still green.

The technical term for leaf yellowing is "chlorosis". That indicates a lack of chlorophyll. But the organelles in which chlorophyll resides, chloroplasts, are present because that yellow pigment is almost exclusively found in chloroplasts.

Something is interfering with the production of chlorophyll.

The 4 major culprits in that regard are 1) overwatering, 2) nitrogen deficiency, 3) a micronutrient deficiency, 4) soil parasite.

1) Overwatering -- I doubt it, given where you live and the pot volume.

2) You're growing the plant in bull poopie -- rich in nitrogen. Ah, but what form of nitrogen? If it is fresh poop then some portion of the nitrogen will be in the form of uric acid and/or urea and/or ammonia. These chemicals are toxic to plants and affect root function, too. Old poop is okay under almost all circumstances because if it is old it releases nitrogen very slowly as compared to industrial fertilizers or fresh poop. How do you tell if it's old or fresh? If it smells like crap, it is. If it smells like sweetish dirt, it is. Old poop smells like sweet dirt.

3) Micronutrient deficiency -- possible, depending where the bull poopie originated. If east of the MS river it can have Zn, Se, and Mg deficiency depending on how the beasts were fed. If wet of the Mississippi it could have a calcium deficiency.

4) Root parasite. You're screwed.

The simplest solution, IMO, is get down close to the soil and take the sniff test. If it's smells like vegetarian *****, you're screwed. If it smells like sweet dirt go to the next step.

Go to your local garden store and ask for a low NPK, micronutrient fertilizer. Follow label directions and apply. Why low NPK? Because you're growing the plant in old bull poop, it should have plenty of available bio-available NPK. Over-fertilizing will kill a plant.

The easiest way to grow tomatoes is by reading "Organic Gardening Magazine" and follow their instructions to a "T". (Is that still published? I loved that magazine!). It's great bathroom reading.

Bot