what's makes an orange or yellow pepper different than a sweet green peper?

Answer 1

Green" peppers are not some distinct type that happens to be colored green: they are simply immature peppers. Virtually all "green peppers" will, if left to grow on, eventually turn color, usually to a red or yellow shade. Naturally, it is only mature peppers that have the full flavor and, above all, avoid the astringent bitterness of the under-ripe "green" pepper--which is nothing but a relatively late-arrived growers' trick to get peppers to market sooner, even if they are quite bitter. If you want good flavor and eating qualities in your peppers, stay away from picking them green (unless you have some definite want for a fairly bitter and not very sweet pepper). However, they are still a bit sweet.

Answer 2

If you pick a green one and let it stay in the sun on the window sill or if you leave it a longer time on the pepper bush, it will turn yellow and then red.