What Causes Brown Color On Skin Around Spine?

Hi, may I answer your health queries right now ? Please type your query here...
A few years ago, I noticed that the skin surrounding one area of my spine (middle region) was discolored--sort of brownish. I have been checked for scoliosis, and the doctor said that I did not have it, and that the discoloration was normal. However, I would really like to know what is causing it and to see if I can do something to return that skin to normal color. It looks unhealthy, and it makes me self-conscious.