Green peppers that lack the proper amount of calcium develop black, leathery patches. This condition is called blossom-end rot. Insufficient watering prohibits the plant from absorbing adequate amounts of calcium from the soil. Adding additional calcium to the soil doesn't help if the plant doesn't receive enough water.
During the ripening process, peppers exhibit a range of colors. If the black areas of the pepper are not either leathery or soft and squishy, it is merely ripening to a different color. Many peppers start off green and turn black before changing to red or yellow. Some peppers mature to a purple color that is often referred to as black.