To tell the truth, I never use black, unless I am drawing a black cat or something. I always use other colors because in nature, shadows are never truly black. Have fun and experiment with color. For example, in a red shadow, lightly layer on a dark evergreen - it'll create a richer depth than black ever would.

Do you know anything about color theory, how about color wheels? I can look up some links to help you. Once you have a really solid understanding of what colors are compliments of each other, your shadows will pop more than ever before.

That drawing s off to a very nice start! You'll find that Prismacolors are awesome to work with! You'll also find the technique that works for you. I have two that I use -- very heavy handed in areas, and a lot of slow layering in other areas. Also, experiment using dark paper... Proismacolors are awesome on dark or colored paper!