Wash the peppers under cool water. Cut the stem off the bell pepper and scoop the seeds and membrane out. Place the pepper on a cutting board and hold it so the bottom of the pepper in on the cutting board. Cut the pepper down the center then cut each half in half.
Using your knife remove any remaining membrane and seeds. Lay one of the pieces of pepper down flat and begin slicing it into thin long strips along the longest edge. Place the pieces into a large bowl you continue to slice the entire pepper into strips. Repeat with the next two sweet bell peppers.
As you add the strips from each of the different colored peppers into the bowl toss the pepper slices to evenly mix each variety of bell pepper into the mix. Once you have all of the bell peppers cut into slices or diced divide the sliced bell pepper between quart size freezer bags or FoodSaver bags.
Squeeze as much of the air out of each freezer bag before sealing. If using an food vacuum sealer follow the manufacturers instructions to seal each bag. Place the bags in the freezer. Use within 4 months.