It makes me wonder if fresh meat has been added to the outside to make something that didn't sell look better to the buyer. The color difference you see occurs naturally.
Red meat contains a pigment called oxymyoglobin.
This natural pigment combines with oxygen and changes the color when meat is exposed to air. The inside area of the meat is darker because of lack of oxygen, yet it is just as wholesome as the outer, red area. Fresh meat in vacuum sealed packages is also dark in color until the surface is exposed to air. This meat may also have an unusual odor which will disappear after the meat is removed from the package. Once purchased, fresh ground meat should be used within one to two days for highest quality and safety.