Last year, I was stung by a bumble bee on my right hand. I had a local reaction, but was left with a slight darkening of the skin surrounding the area. Now, a year later, the same area has became sensitive and has turned a dark purplish color. It is not swollen and I have not hit it on anything to bruise the area. The color also changes in darkness. Yesterday, it was a lighter color; today, it is darker. What could be causing this and should I be concerned?