The easiest way to do it is to mark out your squads, put a drop of colour on the bases if you've not started uniforms or markings. Put them on your table, line them up, then quarter the group in a different direction, and paint those quarters with the skin tones you want.
Line them up by squad again, shuffle them, quarter again, and do hair.
I'll try and snap a picture later of my
IG regiment where I've done this for Tanith and Mordians, it does look good if you have a strong uniform on the models.
Warcolours and Wargames Foundry do very good skin tone paints.
Example of use with a bit about how to shade and such:
http://www.dakkadakka.com/dakkaforum/posts/list/657413.page

If you look at the more traditional wargame companies like those who cater more to historical, they're not un-
PC, they're just geographical.
I mean if you go too far back you might find
Nignog Brown and
Jolly Foreigner Tan but it's been a while since I last saw those on the market.