Gotta be a joke, right?
Wrong. They are natural.
As the book The History and Social Influence of the Potato written by Redcliffe Salaman in 1949 which mentions that the potato from South America dates back to 8000 years BC and mentions on Page 1 that it was discovered by Columbus in the Andes. Page 24 first mentions the purple potato.
The Purple Potato also known as the Peruvian Purple potato was thought to be the royal food of the Incas.
So there you are and there you have it!