One thing Semir has particularly been working on is faking the sub surface scattering (sss), for example when light penetrates your skin it scatters around, partially highlighting the near edge of that area. Above is a render of the characters face using mental rays SSS shader, Semir will try other alternatives by using utility nodes.
the reason for a face by face comparison was also to show how i want the skin texture to look. The face on the right is the current look of the character, this is what Semir sent me in an email and the face on the left is the color we're aiming for.