If you like to use pencils, the Skin Tone pack by Lyra is great for a whole range of ethnicities. Apparently they were originally developed for pre-school kids to be able to colour pictures of themselves and their friends so they're a chunky pencil. Blick carries them (
here, currently out of stock but back later this month) and I guess others do too. They're the soft, blendable type of pencil (like Prismacolor) rather than water-soluble.
I tend to use those or Copics if I'm colouring people.