A bell pepper's change in color is caused by the breakdown of chlorophyll, which coincides with the maturation of the seeds. All peppers start out green and change colors as they mature. For example, immature sweet banana peppers are a pale yellowish-green that change to yellow, orange and finally red as they become mature.
When people grow bell peppers, they may notice that some of them start out green and then change to yellow or red as they mature, while others may change to white, lilac or purple before becoming red, yellow or orange. Peppers that are picked as soon as they begin to change colors will continue to ripen indoors when kept in a warm place. Although bell peppers taste better and are more nutritious when they are mature, they can be eaten at any stage of maturation.
Sugars, vitamin C, and other flavor compounds accumulate during the final stages of ripening. For early yields of colorful sweet peppers, it is best to choose varieties that quickly change to their ripe color and flavor. There are far more varieties of peppers that mature to the color red rather than yellow or orange. The best fast-ripening red peppers are "Gyspy", "Lipstick" and "Ace."