This one sent me into a complete panic the first time I saw it.I went into the greenhouse one morning to find most of my plants looking like these pictures.A quick call went out to our local plant inspector who lives just a mile away.He showed up,looked at everything and shook his head.He had no clue either.We took plenty of samples and sent them off to the state lab.I thought Country Garden was out of business.

The boys and girls at the lab must have had a good laugh.Back came the lab report saying;"Your plants have Edema and they will recover".Anyway,this is caused by periods of cloudy,cool weather when the plants fill their tissues with water.Then,out comes the sun and the plants can't get rid of the water fast enough so the cells rupture.It's unsightly but not fatal.New leaves grow and the damaged ones drop off.Damaged leaves do not recover.
Pic is the underside of the leaf

One final shot

So can the problem be avoided by reducing the amount of water we give them on cool cloudy winter days? We don't have cool and cloudy day at any other time. LOL.

I think that would solve the problem.In my case,I always seem to be into that cool,cloudy situation before I start holding back on the water.I have some of that going on right now.Those are new pictures.Fortunately,it only affected a very few plants this time.