I've only made these with green peppers, but there's no reason you couldn't make them with red, yellow, orange or purple peppers.
Since these are a quick pickle, and not sealed and processed, you probably only want to make a jar at a time. But that's fine.
They're easy to make.
Quick-Pickled Bell Peppers
For a quart of peppers, combine...
2 cups of white vinegar
1 cup of water
1 teaspoon of pickling salt
...in a saucepan and heat to boiling.
Meanwhile, remove the stem, ribs and seeds from your bell peppers and slice them lengthwise into strips about an inch or so wide, and pack them into a quart-sized canning jar.
How many peppers you need will depend on the size of your peppers and your packing skills. Figure 3-4 peppers per jar, but you could use more or less.
Pour the hot liquid over the peppers. Adjust the peppers to let out any trapped air. You want the peppers completely covered with the liquid.
If you don't have enough liquid, add hot water to top it off. Put the cap on the jar and let it sit until it's cooled, then refrigerate it. The peppers are ready to eat as soon as they're chilled.
This is the kind of recipe you can tweak to your liking. Adjust the ratio of water to vinegar to get the tartness you like, or use cider vinegar instead of white, if you prefer. Garlic would be a nice addition. If you prefer something spicier, add a hot pepper or two to the mix.
If you want to make preserved pickled peppers, use a tested recipe from a canning/preserving book, since the acid level and amount of salt are critical when you're trying to preserve foods.