I've been using the tonal colouring technique lately - here's a quick guide.
Black & white to start...
A 'colour' layer to bring the shades closer to skin tones.
'Multiply' and 'colour' layers to block in skin tones.
A 'normal' layer to add more detail plus 'overlay' and 'colour' layers for mottling and hilights.
More 'normal' and 'overlay' layers to add hilights and details.