Smugmug have a very good article on correcting skin tones (prior to printing, but it applies to monitor images ) .
"Use the eyedropper tool of your software eg 5x5 sample area of subjects' skin; only look at the CMYK values; then most all you need to know is that you can never let the yellow % fall below magenta % on anyone's skin unless you're trying to show sunburn !. Cyan should be about a third of the Magenta value"
Here's a link to the PDF article (I use the "Easy" correction method) - free download -->
http://help.smugmug.com/customer/por...3363?b_id=1644