How do you use colors to lead the viewer's eyes when looking at your design? Do they start from light to dark colors or dark to light colors?
what I would suggest is do a version in black and white, that way you can see where the eye gets drawn to without having the colors distract. Then you use color to place over the B&W. Your color choices will be easier to decide upon when you have all your value in place. After your comfortable with black and white your color choices will become second nature. I use a website that helps me pick a color pallete around a single main color, that helps alot also.
Torrent Richard Keyes' Gnomon series on color theory for a short tutorial on the attributes of color and different types of contrasts and harmonies.
There's a bit of art history in it and the examples he walks you through are all paintings, but it should give you some idea on how to use color as a composition tool in your designs.