The bell pepper has many color and it can be green, red, yellow, orange and, more rarely, white, purple and brown depending on when they are harvested.
Variety + Time of maturity= color
Bell Boy (70 days to harvest; goes green to red)
Lady Bell (72 days; goes green to red)
Purple Belle (70 days; immature purple, black to red)
Chocolate Bell (75 days; green to chocolate brown)
Gypsy (65 days to harvest; pale yellow to orange to red)
Sweet Banana (70 days; pale yellow to orange to red)
*Fruits may be harvested at any size desired. Green bell varieties, however, are usually picked when they are fully grown and mature—3 to 4 inches long, firm and green. When the fruits are mature, they break easily from the plant. Less damage is done to the plants, however, if the fruits are cut rather than pulled off. The new, colored bell pepper fruits may be left on the plant to develop full flavor and ripen fully to red, yellow, orange or brown; or they may be harvested green and immature. Some (including "white," light yellow, lilac and purple) are colors that develop in the immature fruit and that should be harvested before actually ripening, when they turn red.
Hot peppers are usually harvested at the red-ripe stage; but "green chiles," the immature fruits, are also required for some recipes.