Maybe these will help. My daughter swears by them and she is quite the artist; I've used them on occasion when I'm really stuck:
http://www.colormatters.com/colortheory.html
http://www.realcolorwheel.com/rcwchart.htm
This one instructs on how to create a color wheel;
http://daphne.palomar.edu/design/cwheel.html
Hope it helps :)