The "normal" white is actually blending white. Pigments can be added to it just like a base. In fact, many of the Magna discharge formulas call for blending White as the base. It can also be used as an underbase for shirts that do not discharge as well (instead of a neutral base). Colors the background enough and yet remains very pliable and soft hand.
Why Magna doesn't actually call it blending white I do not know. They do call the ULF (non-formaldehyde version) blending white.
Super white is used as an opaqueness white discharge.