Why are my cucumber and courgette plants leaves paling in colour?

[Baldy]

cucumbers hate the cold more nearly anything, I never do well with them unless I sow them late

They're very prone to topping themselves given the slightest excuse... tis too cold for them to be out I'd say...
Balders

[Bal]

I've had mine in the green house for about a week now. I cover them with fleece every night. I have now started to put heat in the greenhouse. The lowest temp last night was 9 degrees in there. Will that be ok for them. I've still fleeced them even with the heater on

[rhyswales]

I've had mine in the green house for about a week now. I cover them with fleece every night. I have now started to put heat in the greenhouse. The lowest temp last night was 9 degrees in there. Will that be ok for them. I've still fleeced them even with the heater on

They should be okay in a heated greenhouse. Although 9 degrees is still quite cold for cucumbers. If it starts getting any lower than that they'll soon start getting like the op's.

Try and bring them in overnight if you can, looking at the forecast were still due for some cold nights.