Last year I grew jalapeños. The fruits were tiny, but I was able to harvest a few handfuls. I noticed that many of them started to turn black on the plant. They were still edible, and they weren't rotten. The skin of the fruit developed black patches, shiny like the rest of the skin. It looked as though they were ripening to black (instead of red like other peppers would). The plants looked perfectly healthy otherwise, and continued making fruit.
Is this normal? If not, what causes it / how can I prevent it?
(Sorry, no photos available, I didn't think to take pictures at the time.)