If you are pretty good at drawing already I'd suggest to practice at color drawing for some short time using your intuition and your eyes, and then move on to the serious stuff. I mean color theory. You might find useful Gnomon Workshop tutorials on color theory and Johannes Itten's "The Art of Color". Also, here you inevitably will need guidance in proper usage of your instruments, so find yourself a manual for the technique you use (some book and I find youtube videos on topic pretty useful ofttimes).