SO was this a ms-64 cent that was cleaned from dark brown to a light copper color then left set for a few months to cause the red to comeback some
Copper is typically recolored after it has been dipped n' stripped because no one wants ugly pink copper
Most cleaned copper is left to retone naturally to a brown patina. Generally, you can tell if the patina has been messed with because natural brown and cleaned retoned brown almost never look the same. Natural patina should be fairly uniform, not spotty or streaky. Retoned patina may also have some color to it that would not develop naturally on circulated copper. These patination differences occur because stripped copper is very reactive and rapidly oxidizes.
Retoning can also be caused with the addition of darkening agents. One popular commercial product is known as "Deller's Darkener" and there are homemade recipes as well, many involving the use of sulfur.
These can be a bit trickier to detect and experience gained by looking at and holding as much copper as possible is your best defense. If you look at enough slabbed examples(or even unmolested raw coins) you will get a feel for what shades of brown should occur and what is the average natural appearance.
Retoning copper to Red is probably the most harmful form of copper coin doctoring simply because of the huge differences in value between Brown, Red-Brown, and Red. Once again, the experience of examining natural Red copper in hand is your best defense. Brown is more or less Brown but Red can range from a brassy yellow-orange to fiery deep red but pinks, bright oranges, or other day-glo colors are not normal. As far as retoning copper back to Red, I think that would be the most difficult type of retoning. More than likely, it would be done through chemical means.