At this point, I freeze the cookies on the baking sheet for about 15 minutes to make them easier to cut and handle.
Set aside 1 tbsp of the royal icing in a small bowl and cover it with a damp tea towel to prevent it from drying out.
See my tutorial on How to Make Easy Royal Icing for Decorating Cookies for instructions on royal icing consistencies and my How to Decorate Cookies with Royal Icing for outline + flood how-to's.
You'll notice that there are a few air bubbles in the brown icing on my cookie. These are caused by mixing the icing rapidly (usually when adding colouring).
I was in a hurry to get the icing on the cookie (busy day!) and didn't gently stir in my food colouring (I pretty much whipped it). Take your time & you'll be fine!