I blend (with a blending pencil) and i burnish in between numerous very thin color layers.I like to push things to the edge,thats why i exaggerate in details and colors. I alter colors to my preference, and if details are not enough then i invent some. Its like you put the human skin under a magnifying glass...does this make any sense?
my last question would be: what pencils do you use for that? I use Polychromos from Faber Castell and Caran d'ache, I think they are fantastic, but I have always have probs with the skin color... maybe because of that I prefer drawing with the grey colors on black paper. I tried about ten portraits in colored pencils on bright paper, but am totally unsatisfied with the performance, the pics look never so lively and naturally like yours.