Here are some short, really clear and concise vids that will walk you through basic FCP Color Correction. All around 5 min. each. Couldn't be easier to understand.
Part 3 specifically covers white balance, but I recommend watching them in order, because he explains, for example, how the scopes work and how to correct skin tone, and these are valuable lessons.
Like every other element of making a movie, color correction and effects are an art form. I can do it competantly, but I can't do it artistically.
I'd like to know how these things were done before computer generated coloring and effects. I love seeing the before and after footage of high end Hollywood projects, where you think the footage couldn't possibly be usable. It's incredible.