So you're new to the forum, didn't post any examples, don't have a sketchbook, have a friend but for some reason can't ask him/her, and you want in depth answers from professionals. I don't think you're really serious about it. It would be like asking "How does Bernini sculpt like that." We have no idea what level you are at so the information offered might be a waste of our time and may hurt your development. Paint something from life of photo, post it, and I'm positive you will be helped here.
You actually had about a dozen explicit or implicit questions, which is a good sign - you have an enquiring mind! If you just ask questions like these ones you'll get plenty of "rules"/opinions, however if you focus on increasing your own basic understanding of colour and light you'll be able to work out for yourself the answer these questions, along with the dozens of others that will go through your mind every time you paint.
From what you've written I think dpaint's suggestion of James Gurney's Color and Light would be the best starting point. That together with my own site (liked below), plus plenty of experience putting this information to work, hopefully should point you to the understanding you need to answer all of your questions. There's also a link to a colour theory discussion thread if you'd like information relevant to any specific questions (one at a time, please!).
Thanks again to dpaint, ezion and briggsy, for the advice. I get now after your answers and asking some other painters in personal how they do it that it's a lot of trying for yourself instead of finding THE rules who decide how to do coloring (it's a bit of a flaw of mine to search for definite rules I can follow in everything).
Saw your huge thread, briggsy, read a bit in it and almost asked in there but then it looked too abusive so I made my own
Jason, I get your point and of course you can't give too much help here without examples and stuff. My main request just was to find a guide and/or very general advice how to get started cause I felt kinda buried in information and threads and tutorials but well, somehow seem unable to find a single one about f.e. how to choose skin colors.
Well now I know that it isn't that simple, can't be answered in general and that it is work I have to do on my own...finding out and stuff. Experimenting with color.
But I'll surely come back when I have more specific questions (with examples then )
Most of the time, when people have trouble moving from monochrome to full color, it's a chroma problem.
Wait. I want to know more about this. Do you mean things like not understanding the value of a particular color because of its intensity? (I apologize for what is most likely horribly inaccurate language.)
The reason for all the controversy and confusion is you've (The Original Poster)inadvertently asked one of the most complex questions in all art-How to depict convincing skin surface using paint especially inrelation to colour.
After you've read your colour theory primer and actually done the practice exercises with the paint the question you might ask yourself then might be "out of all the ways of painting flesh that there has been which one will I start with?"
A good starter book on this quest would be "Color for Painters" by Al Gury.
P.S.If you get that far ask me anything as I am an expert on the subject and that's 100% a factual statement(Yes,just to confirm the last statement IS IRONIC!)and when you've finished the Al Gury Google Turbid medium method and when you've finished that................you get the idea.