All Bell Peppers Are Essentially the Same
Red, orange, yellow, and green bell peppers are all the same type of bell pepper, they are just in different stages of ripeness. Bell peppers start green and then ripen to yellow and orange and then finally to red.
With that in mind, different strains of bell pepper are bred to favor a color. So some strains a bred to keep from ripening and stay green, while others are bred to ripen to a red.
Further it is worth noting that in practice, and in a culinary sense, the different stages of pepper color all correlate to different tastes. So in a culinary sense one may consider the peppers to be of different types, even though botanically speaking they are all the same fruit at a different stage of ripeness.
FACT: Bell peppers also come in white, brown, and purple.
FACT: A bell pepper is a type of fruit, a berry, botanically speaking. This is true even though they are commonly treated as vegetables in the kitchen.
FACT: The vitamin contents of peppers change as they ripen, so for example red bell peppers have 11 times more beta-carotene, about two times more Vitamin C and ten times more Vitamin A than the first-harvested green bell pepper.