Bell Peppers

Bell peppers are Botanically classified as fruits (since they develop from flowers and contain seeds), they are commonly treated as vegetables in cooking.
 
As they mature on the vine, they turn yellow, orange, then red (or other hues like purple in some varieties). Riper colored peppers tend to be sweeter and higher in certain nutrients.
 
The reason why red and orange peppers are considerably more expensive in the market, it's because they take a lot longer to go from green to red and orange. The longer the fruit is on the vine, the more susceptible to sun burn and pests.