Recurring Discoloration Starting In Leg, Foot, Ankle Creeping To Knees. History Of Twisted Ankle. Any Ideas?

hi . for some time now (for approx. 5 years or more) I have had a small issue that has started to really worry me for it s frequency in occurance; basically there is a discoloration that appears almos as dirt crusted into my skin but it isn't dirt and won't wash off no matter what I do. this happens usually starting in my right leg around the top & side of my foot as well as covering my entire ankle as well as creeping above at times (a few of these times going all the way to my knees) and has appeared many times in my left foot and lower leg as well. medical hist is nothing dramatic, only item of note was that 2 yrs ago my ankle (right) was badly twisted (was told by doctor at time that it wasn't broken) and both of my legs from the knees down turned this discolored state for a solid 3 weeks. each time this occurs the duration varies but it never completly goes away, just gets progressively worse . this is not usually associated with any type of pain however.