Here is a close-up of the leaves on the Roma Tomato

This is the Lemon Boy(my apologies, I put in yellow boy in my OP and it's Lemon boy)

And here is a close-up of the Lemon Boy's leaves; these are healthy ones at the top, that have those dark/black spots I've been seeing in the yellowing leaves.

The Roma does not have these dark spots in its' healthy leaves.

Too much rain or over-watering, which in a container that small would be easy to do. Other possible causes are lack of nutrients - primarily nitrogen. You must feed them regularly. Or being root bound in the pot. That is a big plant for that size container so it could easily be rootbound.

Every time you water a plant in a container the nutrients leach out so they must be replaced regularly. When the size of the container is proportional to the plant you don't have that much of an issue.

Dave

Hi Dave! Thanks for replying; I decided to give them some plant food with their water today, here's hoping that it will help them perk up a bit. I didn't even think about how they might need plant food already; the nursery I got them from has the same tomato plants and they are doing fine.

I'm going to try to transplant them into a bigger container if I can-I don't have a lot of garden space available. I have 4 more little 4" tomato plants, but they're healthy.

Notey

Most container growers recommend feeding weekly. Using liquids is easier as you can just mix it up once a week when you water. others will use 1/4 to 1/2 strength mix each time they water.

Dave

I'd also like to mention I have potting soil, it's osmocote and it claims to feed for 6 months; would you advise I supply additional feed weekly, or should that be okay?

Notey