The black you see is just the heat shield cover the original exhaust muffler system was chrome. The Black mufflers were only released on the special eddition 500 Rocket X but the high performance Black loud freeflow cat free exhaust that look identical to the stock ones are sold as Accessory TORS which allow a power increase with a modified filter and air inlet with a tune download.
They do indeed look like UK import Dave Platt slip ons that also came with an optional crossflow pipe in various muffler lengths. These are also sometimes provided in black powdercoat or paint.