First Charles, let me clear something up. You said you were aware of my myriad floss. I have false teeth so I don't even use floss. Let's try to keep this blog real, okay?
That said, I agree with you about the creation of all those grey characters - which is to say, all characters - but particularly those who are a darker grey. Once in a while, I'll create a total bad guy, such as Sarah Byrnes' father. He's a guy I just want the reader to be scared of. His job in the story is to make Sarah's life risky. When I do that I show him only by his behavior and let the reader decide how he got that way. All I want in that case is malevolence. Even then, however, I have an idea what his history might be or what brain chemicals might be mixing in a toxic way because in the end, if the reader doesn't believe him, my story is in jeopardy. In my soon-to-be-released (finally) book, Period 8, I've created a psychopathic character who raises all kinds of havoc in the lives of unsuspecting peers. I had to let his psychopathy out a little at a time and I had to keep in mind that he objectifies all other life. No empathy. That's a character I can't relate to in general, but paying attention to times in my life when I've been embarrassingly cavalier about other people's feelings to meet my own ends, helps. Beyond that I need a deep understanding of other characters' responses to him.
Like you, big Chuck, I'm often asked about writing, by individuals trying to break into the business or in more formal, writing workshop arenas. I refer them to On Writing, by Stephen King and Bird by Bird, by Anne Lamott, because the information in both those books is invaluable. But then I turn them inward. It's important to know that you have to "just write it" and that about eighty five percent of modifiers should be edited out. It's important to know the different ways different brains are capable of structuring story and character, and how your particular brain works. But to me the most important character in your story is the character writing that story. I need to know as much about myself - how I operate, my biases, my agendas, my strengths and floss, etc - as I know about any character I create, because my understanding of basic human existence will float or sink my story. For most of us the most basic human is us: me. Which means I have to back up to see the whole picture at the same time as I go deep into my own understanding so I can bring that certain brand of reality to the reader.
That's a little obscure, but if I can ever articulate it clearly I will be a rich, rich man. At which time I will send you flowers.