not enough sun? too rich a soil? I've seen them go green because the tomatoes nearby got fertilized.

I've seen 2 different kinds of purple leaf basil. I've grown both. The one I like the best is curly purple leave basil. It maintains the purple much better than the other one. I do like the swirls of green in the leaves, but I like the solid curly purple one better. I have noticed when it gets really hot, like in the 90's there are a few leaves in the curly one that get streaks of green in them. But none of the leaves on either plants have gone solid green. Most of mine get 8 hrs of sun. I have had them where they get about 5 hrs, but I haven't noticed any difference in how much green the leaves get. I've been growing the purple basil for 5 yrs now, but the last 2 I've just had the curly leaf kind. All mine are grown in flower beds or pots, which aren't near any of my tomato plants.

Kat