If the coin was in the NE (new england area) a long time, the sulfur in the air can alter the color of a coin. If it was in a cello for a long time they can also turn colors. (usually not yellow) If it was in a soft flip, they can turn purple in color because of PVC damage. But the patterns remind me of a coin that was out in oil and partially dried, but some of the oil prevented the tarnish from happening, thus the differences in color. So without know how it was stored for years, it could be any ones of the events I mentioned.