Changing yellow in colour and small dark patches are common as plants send their nutrients to the grow tip and of course their fruit.
I recommend that you remove lower leaves - gradually over a period of a week or two - up to the first truss. However, if you don't have a first truss yet, keep things as they are so as not to stress the plant.
By removing lower leaves your plant will get:
- Better air circulation around the base of their stems
- Less bug activity
- Less chance of fungal disease
- More energy for the fruit and top growth
- Earlier ripening
This applies to tall (cordon, indeterminate) plants and not bush varieties. However, if you see yellowing or damaged leaves on your bush plants, I would remove them too.