Most peppers will darken if given enough time in the season. I've been canning my banana peppers in a pickle type brine, hot and sweet. Seeds and all. Throw in some red pepper flakes, clove of garlic, and maybe a tsp of ground cayenne and they're all spicy! Some say they taste very similar to pepperoncini.
All other mild or sweet pepper I de-seed dice and freeze to be used later in cooking dishes like meatloaf, eggs, stir fry, and salsa. Thing where texture wouldn't matter. It's my understanding that hot peppers can be frozen whole.