Coloured wood primer/undercoat?

[Eiron]

All the tins of wood primer/undercoat I can find are white. As I'm putting black gloss on top, it would make life easier if I could find a darker primer, as the white shows through a single coat of gloss. Does anyone sell black wood primer? Or can I add some pigment to the (B&Q) primer to make it black? Blackboard paint? Gloss? Soot? Photocopier toner?

[mark]

Use wood primer, then a dark undercoat.

mark

[Stuart Noble]

Toolstation do a grey primer. Just used it on a new front door.