Three different-colored Thai curry pastes, how are they different?
Thai curry pastes can have a variety of ingredients, depending on the style and region. Some of the most common components, however, are shallots, garlic, chiles, lemongrass, galangal, fermented fish/shrimp. The chiles give the color: a red paste is made with dark red (dried) chiles. Green is made with fresh green chiles, and yellow with light red (dried) chiles. The only other pigmented ingredient in curry pastes is fresh turmeric, which gives a brighter color, and makes the paste yellow when combined with bright red chiles.

Green is usually the hottest.