The "WhiteTRF" foil covers black toner to about 96% which means there is a very slight "off-white" but glossy effect. The human eye doesn't notice this very slight offset IF there is no "pure white reference" nearby. So for most all applications, the 96% white is seen as pure white... all day long. Looking at this white foil over the black toner image on the bag, your brain says that's pure white because there is no painted or otherwise pure-white reference. Now, put a reference next to it (see the Budweiser pics) and your eye can definitely see the difference. What we've done here is to apply a second white foil over the first. White is the one foil that you can make stick to itself. Since the base-white it's 96% white to start with, the second white is effectively "pure" white.
Since it's a bit of a hassle to do, look first to see how ONE white foil looks on your project. If you want a pure white "double-white"... here's how to do it: