Is there any difference between green, red and yellow bell peppers, barring the color?
Normally when I buy a pack of 3 I always leave the yellow till last. It's normally due the coloring looking less appealing in the dish.
Same plant species, different cultivar, different maturity, different tastes, different nutritional value. To summarize from the link, green are harvested earliest and contain the least vitamins, yellows are next and contain more vitamin C and less vitamin A and beta carotene, reds are harvest last and contain the most each vitamin types. Yellow and red are both sweeter and more fruity than green.
As a greenhouse operator, I can tell you that the first answer was the correct answer. Green peppers are really peppers that are picked before they are completely ripe. All green peppers, if left on the vine will transition through yellow and end up red. This is why a green pepper is more bitter than yellow, orange or red. Yellow and Orange peppers are loaded with Vitamin A and C while Greens have none or very little. Green peppers are generally cheaper to buy than the others because they don't have to stay on the plant as long.
Seed developers have found a way to make pepper plants ripen to either yellow, orange, chocolate, purple or red depending on which variety you have.