yes a black base has a higher graphite content which does make it faster. but the wax does not, for example the best super high fluorocarbon waxes are usually white powders. they are most hydrophobic and have the best temperature range.
Important note however, just because you have black base material doesnt mean your base is a super-fast race base with any special properties - you can get black pigmented extruded-piece-of-shit bases.
Yes, like Swix HFBW (I guess?). But to be honest I don't really see the point in using HF waxes for freeskiing (unless you ski mild slushy conditions and are competing for X-games gold). I mean come on, these waxes cost 60+ USD for 40grams.