It comes from research. For dark colored vinyl to be cool in the sun, there must be some type of clear membrane that reflects most wavelengths that is normally being absorbed. I would say with microfibers and all that they have that design down. I wish they had it in leather as my car seats are hotter than the dickens until the AC flows through them.
http://scienceline.ucsb.edu/getkey.php?key=4010