I use black tinted with whatever colour suits whatever I'm painting ie: Take a black painted Albie fuselage, the wood areas would be tinted with a brown or buff, the metal areas with a slightly darker grey even a hint of blue, or green/grey of the underlaying colour (or as it would be). Blacked metalwork, guns, cylinders etc I tint with greyBlue, quite heavily. Rubber items with red brown.
I've often used panzer grey, with a black ink wash to highlight details, it's a matter of taste really though.
Look at most black objects, see what the natural tint is, like tyres etc, never really black.
Keith.