Please, oh, please forgive me for using an unscientific term "misting". Sure looks like someone misted them to me.
At the HL, I found in the description for Blue Ivory the term a green "blush" in the margins.
Now I'm blushing!!!!!!!!!!!!!
Whatever you wish to call it, I have it occasionally on El Nino, Blue Ivory and Great Escape. I have it on some of their leaves right now. I've had El Nino since 2003 so it isn't a question of maturity, and here it is today, so it isn't a question of Summer heat or sun for me. Just the variation in the leaves.
-Babka
{{gwi:959475}}
Wait! There's more...
The HL data base for Allegan Fog uses the term "misted" and in that hosta it is not transient, so I haven't gone completely bannanas.
Babka NorCal 9b