The color can be green, red, yellow, orange. Red, yellow, and orange peppers all come from different seeds and are different cultivars of pepper. Red peppers are simply ripened green peppers.
Green peppers are less sweet and slightly more bitter than yellow or orange peppers, with red bell peppers being the sweetest.
The taste of ripe peppers can also vary with growing conditions and post-harvest storage treatment; the sweetest are fruit allowed to ripen fully on the plant in full sunshine, while fruit harvested green and after-ripened in storage are less sweet.