Your typical royal icing recipe, ideal for cookies.
2 Tbs meringue powder
1/4 cup water
2 3/4 cups sifted powdered sugar
Paste or gel food coloring as desired
In a bowl, beat meringue powder and water until combined. Beat in powdered sugar. Divide into smaller bowls and tint as desired with food coloring.
If you're having a hard time finding meringue powder and paste or gel food coloring, check out a hobby store, such as Jo-Ann or Michaels or take a look at the Wilton website. I personally use the 8 Icing Colors gel coloring set from Wilton.
CREDIT: Better Homes & Gardens Special Interest Publication - "100 Best Cookies - Our Most Popular Holiday Recipes", p.69, c. 2007