Anyone know of a screen protector for the rear glass that adds some grip and is clear? My GF is complaining of her phone sliding on some surfaces. I'm specifically looking for one that would allow you to see the color underneath. Doesn't need to be optically clear, but does need to show the color. And of course, the surface must be grippier than the glass. I've searched, but I get flooded with hits for tempered glass protectors...