I think you should worry about value first. Learn to render the form properly and then start doing colors studies (from life, photos, and master paintings). Color can't be mentioned without bringing up "Color and Light" by James Gurney, because that is, in my opinion the best art book ever, so I suggest you look it up. Although it might be a bit advanced for you right now.
But yeah, study value. Learn what makes forms read well. Here's a good place to start
(don't forget to check out parts 2 and 3, linked on that page).