Possible Clues:

• Does this mean to have nil in the skin?
• Plan to absorb litres in skin pigment
• Pigment causing tanning
• Freckle, essentially
• Have a meal at the inn when it's dark for the hide there
• That'll make one dark if it's only skin deep
• That's what makes one skinny in the dark, perhaps
• How people make it dark around the broken nail
• That makes men dark about a crooked nail
• Pigment in the skin