Walk down any populated street, and there will be huge variety of variations of flesh tones.....
Here is an article of the different types of skin tones, and a paint breakdown on how to get there.
Thanks to Chrispy on Cool Mini or not, lots of work went into that guide.
Next one off the rank is Model Works by Chris Clayton. his large scale female sci fi soldier SBS is a great piece of work (I've linked to the face stage, rather then the construction) and his Space Marine build and paint is also highly impressive, both in details and how to.
And the third off the rank is the Heroes and Villains blog, which gives a SBS on painting complicated, fine patterns. such as on check or tweed.
Definitely worth the time to sit, read, note and then practice!!