Suedecloth is used as the layer closest to baby's skin, it is a polyester fabric so does not absorb any moisture, but instead wicks it through into the absorbent part of the nappy, and away from baby's skin. Because it does not absorb moisture, it feels dry, keeping baby's skin dry.
Microfleece is used for the same purpose and is a matter of personal preference as to which one you use. Suedecloth is known for being the cooler and less bulky of the two, and is the most preferred in Australia and warmer climates or times of year, with microfleece being warmer and better for the cooler climates and times of year.
BLACK - Black has residual dye in it. It should be pre-washed prior to use, as it will leach if not pre-washed and discolour any other fabrics used in the garment or in the wash cycle. 2 wash cycles should see all residual dye wash out and ready for use.