Chilli peppers are typically red, but they can also be green, yellow, orange, purple or brown depending on the variety and the maturity of the fruit. Some chilli peppers, like the Thai bird's eye chilli, start off green and turn red as they ripen, while others, like the Caribbean habanero chilli, can be orange or yellow when fully ripe. The heat level of a chilli pepper is not necessarily determined by its color, but by the amount of capsaicin it contains. Capsaicin is the compound responsible for the burning sensation we feel when we eat spicy food.