So yes, chilis get hotter as they ripen (that is, as they turn from green to red). Many chili varieties are picked and sold in stores while still unripe and green (e.g. jalapeño, serrano, poblano), but you will occasionally see ripe, red ones in stores.
Thereof, what happens to jalapenos when they turn red?
Jalapenos are ready to be picked when they are firm and bright green, but you can leave them on the plant all the way until they turn red. Red jalapeno peppers are sweeter to the taste and not quite as hot, though they absolutely retain their jalapeno heat and flavor.
Why do jalapeno peppers turn red?
The big difference between these two peppers is simply age. They are the same pepper, just a green jalapeño is picked early in the ripening process, while a red jalapeño is left on the vine to mature. During the ripening, the jalapeño, like other chilies, changes color from green to red.