I think the purple basil is a hybrid and when started from seed you don't get the same quality plant...it slowly looses the characteristics that it was hybridized to have. But some articles I have read say that there is a chance the purple can be maintained by making sure the plant is getting at least 6 hour of full sun, they might be lacking nitrogen and possibly the removal of the green leaves is supposed to help the plant maintain the purple color.
Hi Rick, I notice that my basil (purple ruffles) tends to turn greenish if I have let it dry out too much and it gets stressed. I have some growing in the ground in a high tunnel, but not close to the drip irrigation and it dries out more than I ought to let it. Then it starts to change color. It is growing next to the edge of the tunnel and can get rain, now with all the rain we have been getting and it is quite a bit cooler, it is much darker than it was.
