Whenever I use a silhouetted image, I like to do what I call "the silhouette treatment". I learned this from the fabulous Michelle Zindorf. This is a very simple technique that adds a lot of "pop" to silhouettes.
First, I try not to use black for the silhouette images when I can. I often use Night of Navy. After I stamp the silhouette images, I use a fine black marker to draw a small line anywhere on the left edge of the image where I shadow might be (skip this step if you stamped the silhouette image in black). Next, I use a white gel pen to draw a small dot or line anywhere on the RIGHT edge of the image where a highlight might be. That's it! Let's see what the end effect is.