Hey DanW,
One of the main reasons for your basil leaves turning light green could be over watering. Secondly if the soil is of low quality, it could also be the reason for the light green color of your basil leaves. Hence the remedy to that is, you can add slow-release fertilizer so that it will get released into the soil or another option is to add liquid fertilizer to the soil as that provides quick supply of nutrients to the leaves and roots of the basil plant.
