Ok, here is my advise.
Check as many picture references as you can.
Black cloth is not truly black but usually got a bit of another colour mixed in, also how the light reflects of it will change the black to black/purple, black/blue, etc. If you want to go for all-black than you will need to play with the glossines of your paints but that, IMHO, will result in an inferior result.
So work from a medium colour that can be modified for highlitings(dry-brushings) and darkened for washes.
In short mix quiet a bit of your base colour and thus that as a base for your washes and dry-brushing too.
Example:
I tend to mix a LARGE batch of flesh/base colours that are than adjusted per kit and for shading/highlights. Simple reason, it is difficult to mix a second batch that matches the first one correctly.
To get a better image of waht I am talking about, try to get hold of the "Amazing Figure Modeler" mag that features "Lady Z/Zorro", a kit is totally dressed in black, but with the colour variations you can change her shirt to satin vs cotton pants, etc.
HTH.