Heat will do this to an LMC. I tried an experiment a few years ago and put an LMC on my wood stove over the winter. Within a couple of days it had turned a golden yellow color.
"Yellow" is not a color I'd ever associate with a "beautiful" cent. Yellow might be a minor tone in a progression, but if lemon yellow is the dominant color on a copper coin, you can place safe odds that's been treated, heated, or cheated.