Want a real answer?
First off, I assume your are growing in soil. Right?
Secondly, this is in result to the ferts (nutes) you are using. It is high in something, like iron.
Thirdly, Some mexican dirt strains will do this when they get a rich diet. Over doing on the nutes.
In most likelyhood it is your nutes. Years ago you could buy some veg. garden fertilizer from Kroger (King Soopers) that would do this to any strain grown in soil. But mostly outdoors.