m0useanswered grow question 17 minutes ago Some parts look like the beginning of WPM but if it does not wipe off easily it could be dried salts. Are you spraying the leaves at all with anything?
The bottom side of the leaf does look funny. Almost pest like. White fly is what it sorta resembles but not well..Might need other pics.
What was the reason you put DE on the plants? for pests? Looks like they still in veg so you can teat em with a more targeted pesticide if it is pests.