I've had what can only be described as a stain like appearance that runs from my lower left shin to my mid shin for years. The discoloration hasn't gotten bigger or darker but it hasn't gone away in 20+ years. I'm in my late 40's and have had this condition as long as I can remember; at least mid/late 20's. I'm 5'll, 160 lbs with no health issues. My natural skin tone is olive/light tan. What is this and how do I get rid of it? Is there a treatment?