Originally a Mexican street food, enchiladas didn't have a filling -- they were simply rolled tortillas dipped in chili sauce. The version we all know and love today may vary from its origin -- and widely from each other -- since enchiladas can be filled with a variety of meats, vegetables and cheeses. But what enchiladas still maintain and all have in common is that they are topped with a sauce that is either red or green.
These sauces clearly are different colors, but they also have quite distinct flavors since they typically call for different ingredients.
Depending on your taste preferences, green or red enchilada sauce can work well on a variety of different enchilada dishes. Just do be aware that your choice in enchilada sauce will have a big impact on the flavor of the end product.
Green enchilada sauce is generally a mixture of green tomatillos and green chilies along with other ingredients such as spices, onions, garlic and vinegar. The tomatillo is also known as the Mexican husk tomato and is a staple in Mexican cuisine. They can be eaten raw or cooked and are what bring the green color to green enchilada sauce and salsa verde (verde means "green" in Spanish). They have a slightly herbal taste, and are somewhat fruity and tart in flavor.
One mistake people sometimes make is that if the sauce is green it must not be spicy, or as spicy as a red enchilada sauce.
Boy, are they in for a surprise! Green enchilada sauce has green chilis, which include jalapenos (we all know they pack some heat), as well as serrano, which will definitely tip the spicy scale. As with any color chili, they range from mild to hot, so if making your own green enchilada sauce do a bit of chili research beforehand.
As you might conclude on your own, red enchilada sauce is typically made from a variety of red chilies, vinegar and other spices, onions, and garlic. Some "quick" versions of red enchilada sauce may actually use red tomato sauce or paste as a base. Just like green enchilada sauce, red sauce can range from being mildly spiced to knock your socks off spicy--it all depends on the chili.