The color is determined by the nutrients available - specifically nitrogen. In this case likely too much nitrogen. So what potting mix is it in and what and how much have you fed it?

Dave

Dave, it's planted in some miraclegro potting mix, nothing special, and I used miraclegro tomato-specific fertilizer, but only about half of the recommended amount.

Thank you Dave! Also, one of the leaves at the bottom is yellow and slightly damaged, should I just go ahead and pinch it off?

Not related, but you might want to fill that container up a bit more. It will grow more roots and help strengthen the plant.

Good point Chris. Nothing gained by leaving the pot 1/2 full. The yellow leaves can just be pinched off.

Dave

It looks very healthy!

One other thing to do before filling the pot up with more medium is to put a tall stake or cage in there for some support.

Linda

Thank you for the help! Yeah, we planted a large amount of flowers and plants and ended up running out of soil, so we had to fill some pots less than others.

What is the name of the tomato in this picture, the ones with the dark leaves