Leaves bright yellow at stems and green on outside tips. Some are curling and getting brown spots.
Tomato Plant Leaves Turning Yellow From Stem Out to Tip
Certified GKH Gardening Expert
It sounds like early blight. This article will have more information:
If you do not feel this is the problem, here are some other reasons for yellowing leaves in tomatoes: https://www.gardeningknowhow.com/edible/vegetables/tomato/yellow-tomato-leaves.htm