Wait until the plants have matured and bear fruit, which are the desired color. Pepper plants need at least a year to mature. They produce red, green, white and then black peppercorn as the fruit ripens.
Pick the peppercorns off the plant. They hang down in thin bunches and appear similar to a seed pop.
Pick the individual peppercorns off the stem and lay them out on a fine mesh screen. The mesh needs to be small enough so the peppercorns do not fall through.
Leave the peppercorns in direct sunlight for several days, turning them occasionally. The best way to check the readiness of a peppercorn is to try to grind one up. If it is hard and crisp when ground, it is ready to use.