1935 Buffalo Nickel Toning

Welcome to the CCF, DonnaBB. Toning on high grade coins can have a positive or negative impact on a coin. There are collectors who seek out multi-colored specimens for their collections. They will particularly relish bulls-eye toning an toning that creates a cameo effect. On the other hand, uncirculated or proof coins bearing splotchy or speckled toning will be adversely valued.Toning on lower grade coins isn't much prized. Oftentimes it was precipitated by long time storage in older coin albums and/or envelopes that had sulfur content.

To find out more about it, do a search on "toning" on this website and read some prior threads. There's a wealth of information here!

Given that the reverse color of the posted coin is so saturated, I'd suspect it was housed in an early folder or coin board. That said, Coinfrog, the OP's question was more general, it seems and not simply about the posted example.