Black undercoat can make the detail on small scale figures difficult to pick out.  A technique I saw recommended was to undercoat in black and then apply a very, very light drybrush of light grey.  This picks up the raised detail and makes it easier to see where it is when you need to paint around it.  I've done this with 6mm figures and it does make the task easier on the eye.

Thank you, I will try this.