black oil after 2 weeks?

gooood evening gents,
I just recently changed the oil pan gasket in my 77 chevy and 2 weeks earlier I also changed the filter and oil in it. when I drain the oil I planned on saving the 'new' oil and put it back in afterwards. upon pulling the drain plug the oil was black already. after I put the new gasket and pan back I put all new oil in it thinking that the 'old' oil had been contaminated with something.
2 weeks later I checked the oil and AGAIN its black. any thoughts? bad rings? bad EGR valve?
I know it cant be coolant, it would be a yellowish color, right?

thanks for your time,
Cpl. Boyd
USMC