I think the black one looks ugly, but after examining the Romanian Festool page it look like it's all about functionality.
The page says: "Se poate folosi pentru aspirare praf combustibil si sau exploziv din clasele cu risc de explozie St1, St2, St3, in zona 22"
Which means in English: "Dust can be used for fuel or explosive and explosive class ST1, ST2, ST3, in Zone 22" According to Google translate.
So the black plastic is a special plastic that can withstand corrosive materials. Seems the B in B22 stands for black and the 22 for the name of some officially named hazard zone, in whatever country that applies.