You did not mention where you live but nights have been cool and in many areas the cold has turned tomatoes yellow and a bit of purple on the foliage. Protect tomatoes with a covering anytime the night goes below 55 degrees. The other reason for yellow leaves is too much water - especially if the soil is cold. I do think your tomatoes will outgrow their yellow foliage but try to let the soil dry out even if that means an umbrella over the plant right before expected rain downpours. It is okay to snip off leaves when they are fully yellow. Keep growing, Marianne Binetti