Leaves look old. If this is at the base of the plant up to about half way, it can be due to age. Overwatering basil will usually make leaves a bit yellow color, but it also can be due to poor soil conditions. The color is a sure sign of dying leaves.

I am having the exact same problem. My leaves look just like the ones in the picture. Any word on how to fix it? How do I get them back to the dark lush green. My soil is fine and my other herbs are fine. Any suggestions??

I brought some leaves to the local garden store and they told me it was being over watered, so to cut back some of the growth and cut back on the watering. Hopefully that will help!

You might need more sun.If its in a pot, put it in the sunniest spot.Also, if basil gets too cold, its leaves will burn brown to black.