I remember once seeing something about painting cookies before they bake using egg and food coloring. Has anyone tried this? What part of the egg would I use? I would imagine the yolk discolors.
Thanks!

i found this video on youtube. skip it to 1:15 - thats when it starts to talk about using egg YOLK + food colouring to paint cookies

http://www.youtube.com/watch?v=mdp8tQKWYHY&feature=related

i dont get how they got the yolk to go white though??

There is this technique:

http://www.countrykitchensa.com/ckideas/ckIdea.aspx?Occ1Id=&ideaId=177&idea=471&occasion=General%20Cookie%20Instructions

I wouldn't use egg -- too many health issues. You can do just fine using either water and gel colors or lemon extract and lustre dusts.

You can (and I do) paint gingerbread cookies with either whole egg, egg yolk, whole egg + with food coloring or egg yolk + food coloring (or coffee or cocoa) to get dark, shiny surface.
You paint it before baking and traditionally after baking - in the moment you get it out of the oven.

When you paint it with food coloring, you have to be super super careful to have even surface of the egg wash - unless you are going after the marble effect.
Easier is it to paint before with water only, and with egg and food coloring after baking. The color isn't than as dark.

Because all I get here easily are raw eggs, I am super careful how do I handle the eggs beforehand and paint with egg wash not after I take it out of the oven, but 1 min. before - also take out of the oven, paint, return for 1 min.

No idea what you get by painting sugar cookies

There are some people that paint the cookies with thinned dough. I haven't tried that but it looks great.
HTH

Thanks everyone for the replies! When I didn't get an email notice I assumed that there were no replies!
I want to paint th ecookies with students so that they have the chance to decorate them, but there is no drying time. I do cookie baking as a prize option after reading a certain number of books.
Thanks again for your help!

Here's a recipe for Egg Yolk Paint:

1 Large Egg (raw)
1/2 tsp of Water
Food Coloring

Separate the yolk from the white. Put the yolk in a bowl and add water. Mix in your food color. Paint on the cookie before baking.