What Makes The Difference In Color?

The 2011 looks like it turned yellow a bit from circulation. The 2014 looks original in color, but has a fingerprint on it on the jacket. There is also a coin contact mark on the left side of the shoulder. Body fluids can turn coins. (saliva, sneeze droplets, salt from perspiration and probably other things.) They tend to darken cents in color. Here is a coin I pit saliva on as a test coin. I check it from time to time to see if it gets any worse, so far after a few years, it still looks the same.

Notice the darker color on the right side fields.