AH, then the answer is 'no'.
Now I KNOW you quoted the wrong guy in your first post.
The only leather I'm aware that does what you're asking is kangaroo, and that's based on how 'roo whips react to long periods of exposure to sunlight.
Tanned hides such as lambskin, cowhide and goatskin do not fade as readily due to long exposure to sunlight....they'll dry and crack, but not fade.
Of course as a disclaimer, ANYTHING will eventually fade when exposed to long LONG periods of ultraviolet light....but not 'tan' per se. Just look at your car paint job!
Just 'roo hide 'tans', as it has the same type pigment in the skin as a human has that will darken or change color with that type of exposure.
Regards! Michaelson