If I remember my human anatomy correctly, your sphincter is basically built the same as your mouth. And your anal tissue carries the same skin tones as your lips. This also means it is just as sensitive to irritants as your mouth is. (Why else do you think peppers burn as much coming out as they do going in?)
Most times porn looks the way it does because of some exceptional image manipulation. Get a good photographer, some 1500ºK lighting and Photoshop, and your ass could look just as pink in print. No one really looks that good in real life. You are comparing yourself to an illusion.
Making your ass fuckable is really about making it clean and accessible. Learn how to flex your muscles just right when your top is buried inside you to make him go crazy. Concentrate on being one hot fuck and no one will really care what color your ass lips are.