Cucumber leaves might be drying out due to lack of water. Cukes need lots of water as thats what they are made of (90%). The courgettes are fine. The grey mottling on the leaves is their natural pigment and pattern. You can tell by rubbing the leaves, you won't feel any powdery substance.
If you see grey spots /blotches on cukes or squash leaves then it will probably be powdery mildew, when you rub those they will be a gritty powder. If that happens simply spray all the leaves with a mix of semi-skimmed milk and water (9 parts water - 1 part milk).
