Certified GKH Gardening Expert
This is pretty typical to see some yellowing and curling. Tomatoes are very expressive when it comes to their environment and will let you know that something has changed.
Most of the time this is of no concern. Sometimes this coloration can indicate an Magnesium deficiency on the lower leaves. This can be corrected with Dolomitic lime, which provides calcium and magnesium, both.
This article will give you a good run down of what a healthy tomato plant needs: https://www.gardeningknowhow.com/edible/vegetables/tomato/growing-tomatoes-guide.htm