Chillies - black marks!

[ken]

I'm growing two plants of Joe's Long Cayenne chillies in pots. They're outside but have some protection as they are in a cold frame with the top panels removed. The plants essentially are doing very well, but a number of the chillies have black marks or streaks running down them. Could this be a major problem? Or might it just be something like rain marks, or scorch marks where they have been wet and then caught in the sun?

[Primrose]

I grow Hungarian Wax chillies and sometimes I find the occasional one develops a black streak as it is turning from pale green to orange but by the time they have ripened to red the streaks seem to have disappeared. Maybe it is just part of the ripening process in some varieties?
Some of my chillies have been reared in a mini plastic greenhouse and some have been grown outdoors in pots against a house wall so two different environments. And none of them have been subjected to any kind of insect attack so it can't be that.