Yes, ground beef can be pink inside after it is safely cooked. The pink color can be due to a reaction between the oven heat and myoglobin, which causes a red or pink color. It can also occur when vegetables containing nitrites are cooked along with the meat. Because doneness and safety cannot be judged by color, it is very important to use a meat thermometer when cooking ground beef. To be sure all harmful bacteria are destroyed, cook all ground beef products to an internal temperature of 160 F throughout.
Meat contains iron, fat, and other compounds.
When light hits a slice of meat, it splits into colors like a rainbow. There are various pigments in meat compounds that can give it an iridescent or greenish cast when exposed to heat and processing. Wrapping the meat in airtight packages and storing it away from light will help prevent this situation. Iridescence does not represent decreased quality or safety of the meat. Exposure to light and oxygen causes oxidation to take place, which causes the breaking down of color pigments formed during the curing process.