Are green, red, yellow peppers the same plant?

Here is the answer I found at world's healthiest foods:
Most of the differences in bell pepper color stem from
(1) time of harvest and
(2) degree of ripening.
Green peppers are bell peppers that have been harvested before being allowed to fully ripen. Although green peppers usually pass through a color stage of yellow-orange before turning a shade of red, they don't always. Red, orange, and yellow bell peppers are always more ripe than green ones. Bottom line: all of the bell peppers originate from the same species of plant, and they achieve their different colors naturally, not by any artificial means.