Yellowing of skin on radiation site

I had my BMX done in October of 2006 and had reconstruction surgery done at the same time.  I underwent 16 wks of chemo and 8-10 wks of radiation in June.  About 3 months later I noticed some yellowing on the outside of my new boob where one of the points of radiation was aimed.  I didnt think anything of it really and chalked it up to discoloration due to radiation or even some residual bruising.  Then it started to spread.  Now almost 4 years later covers about 1/3 of my boob starting from the bottom side to the scar.  I asked my PS, he didnt know what it was.  I asked my oncologist and he suggested I see a dermatologist.  I was wondering if anyone else experienced this and knows what it may be.