I actually have a Blackstar... and by "infinite new tone possibilities" they mean about two. That aside, I don't actually know how it works. I'd assume it's some sort of slope control or mid-shift control. I'm somewhat partial to the James tone stack with a mid-shift control. Shifting the centre point around (or making it wider, steeper and so on) seems to give the illusion of 'infinite tone shaping' abilities.
Although I'd be slightly disappointed if the patent office actually granted them the ability to monopolize the use of a potentiometer in place of a resistor... Never stopped Randall Smith though, haha.