PSE has written a book called "Philatelic Book of Secrets" which has many interesting chapters, and for some stamps (by far not all classic stamps) they give Pantone colors for the normal light color (which are not always useful) and UV colors for some stamps (which are sometimes useful). There are two volumes of the book, but the 2c 1899 stamps are listed in both of them. You can buy both books as ebook at Amazon
. (The Pantone color for rose carmine is given by PSE as 213U-214U)
Yes, you have to take the stamps out of the mounts to check the UV color. In other countries like Australia or Germany, the UV light is a very important tool to check for color differences which can be hard to tell under normal light.
The thing with the pink back I don't remember exactly, where my sources were. I think this is my own conclusion based on several sources. Pink stamps from that 2c issue have a strong pink back sometimes, while other stamps don't, and I think the rose carmine does not.
Indeed, it would be very interesting to know if the PF would certify both stamps as rose carmine.