When I first learned to add flat dots in my icing, I loved them so much, I wanted to add them to everything!
You can use varying shades of the same color, or different colors.
A few tips for adding dots...
Thin both colors of icing with water to approximately the same consistency, like a syrup. One shouldn't be noticeably thinner than the other.
Flood the cookie with the base color first and spread with a toothpick.
While the base color is still wet, add the dots using a squeeze bottle. The dots must be added to the wet icing, but do give the base color a few minutes to set. Adding the dots right way, especially dark on light, may cause some bleeding into the main icing as it dries.
If the bleeding does happen, don't worry...it's just a cookie! Most people won't notice and just want to eat them. :)
A few tips for adding dots...