My yellow sweet peppers are just starting to turn yellow, but almost as soon as that’s happened, they start to “prune up” just the image shows, what’s causing this?
Hi!
What is happening right now- fruits maturing takes a lot of energy from plant. All the energy goes to the fruits and that´s why leaves are withering. But do not worry- plant is still able to ripe the fruits. You can try watering you plant with liquid fertilizer (for fruiting plants) which plant is able to absorb quickly.
It is a bit hard to see from the picture- is it only nutritional disorder or also some pests (those light spots). It is very important to investigate those leaves very closely. It would be good for the plant if you remove these leaves. It also helps plant to develop more younger leaves and then you can see if there are any changes or are the new leaves healthy.
Good luck with your chilli cultivation and give us some feedback how it goes! 
These look great! Were these ones ripe?