Happy St. Patrick's Day!
What I did was take a St. Patricks Day chocolate mold that I got from Cake Cottage and used it as a mold for my fondant. Now make sure you either dust it well or use a tiny bit of baking spray in the mold so that it will release from the mold. Then use a color similar to your item (doesn't have to be the exact color, but it helps to be close since you will dust or paint it.) and press it into the mold. Use a pairing knife to scrape off the excess so it fits flat in the mold. And you can use two colors as well (see the rainbow with the shamrocks at the bottom of the mold. It makes it so you don't have to paint quite so much).
After releasing them from the mold let them sit to harden a bit and then dust and/or paint (I did both on the leprechaun, his face was dusted and the other parts were painted). For the pain use either your food coloring or petal dust mixed with a little clear vanilla.
For the leprechaun since he was too big for the cupcake you can frost it and lay it on its side and then add the leprechaun so it looks like he is standing up. Or dry the leprechaun completely so it is rigid on top of the cupcake. I just made these quickly for my kids so I went with the standing up version (oh and put a little frosting behind his hat to help it stay up. )
Now go and look in your cupboards to find all the wonderful chocolate molds that you can now use to create wonderful yummy cupcake/cake toppers with. Enjoy!