I have had a crystal palace geranium for several years, always had beautiful lime green leaves. All of a sudden this summer I got one branch with dark green leaves. Anyone know why this would happen? Hard to see in the photo, but it's in the bottom left area.
cyndyeo your plant is showing chlorosis , this happens when the soil is a bit into the alkaline side (alkaline soils) adding iron or iron sulfate may help you to reduce the chlorosis (yellowing) of the foliage, also the yellowing of the leaves could be due to a deficiency of nitrogen, a bit of organic fertilizer will do the trick.
thank you for your suggestions, but I think you misunderstood the problem. This plant is supposed to have the yellow/chartreuse toned leaves with darker green zonals. Then all of a sudden I got one branch where all the leaves are the darker green of the zonals, there's no yellow green. I'm trying to get the yellow green back. So maybe I have the opposite problem, my soil is too acid? And I did fertilize this plant a couple times over the summer with Espoma flowertone, maybe too much?