If you want to paint black cloth, mix up some REALLY dark gray. give it a couple of black washes, then some extreme highlights on the very edges. Note that this technique only works if you paint the armour a brighter colour; if you paint the armour a similar, dark colour , it blends in with the cloth too much.
Glad to hear you considering blue armour

Too many
SoB players stick to the colours in the codex! I chose a gold and turquoise colour scheme for my
SoB and, i think, it has turned out very well. Go for a light blue armour as this will contrast nicely with the black cloth