Photos show front and back of the same leaf.
I'm also seeing very similar symptoms on my ivy geraniums. We got them in from Oglevee for our stock production and potted them up about 5 weeks ago. This yellowing started to become really noticeable within the last week to 10 days. I swung by the Extension Plant Pathology lab on my way here, and based on visual inspection, they don't believe that disease is the problem. We've been able to control all the usual pests.