There are several ways to make royal icing.
One recipe uses meringue powder, the other egg whites and the third is just royal icing mix from a bag. I used the latter for this recipe, as the store where I normally buy supplies was out of meringue powder. As I wait for my order to come, I decided to use royal icing mix instead. You just mix it with water, as much as you need for a desired thickness of icing, then add food coloring to that. So easy!
My Royal icing library – recipes, tips, tricks
Joy of Baking royal icing recipes (both egg white and meringue powder royal icing), video demonstration included.
Here’s Alton Brown’s recipe for royal icing that doesn’t use meringue powder.
Also helpful: Sweet Sugarbelle’s recipe for royal icing (lots of photos). Also check out her instructions for coloring the icing.