There are now several makes of dehydrator, which dry peppers very well both for colour and flavour. You may find one at your local cook shop, alternatively try the internet or TV shopping channels. A fan oven is best for oven drying. Always wear gloves when handling hot peppers. Cut the peppers into strips (de-seeding is optional) and place on a sheet of baking parchment and set the oven to low. Prop the oven door open, if you can, to allow circulation and check peppers regularly.
To dry for Chilli powder/paprika slice the fruit open and remove the seeds. Chop the fruit into small pieces and place in an oven dish lined with baking parchment and dry in the oven or dehydrator. Once dried, grind into a powder either with a pestle and mortar or a coffee grinder but wear goggles and a face mask as the fine dust can be a severe and painful irritant. Make sure you clean up carefully afterwards! Salt can be used to remove any traces from under the grinder's blades or your breakfast coffee will give you more of a wake-up than planned.
Customers report good success by open freezing whole peppers and popping them into freezer bags once frozen.