Mix together butter, sugar and brown sugar with a hand mixer on low, until light.
Add eggs, milk and vanilla extract and beat until well combined.
Stir in orange zest and cinnamon.
In a separate bowl, stir together flour, baking powder and salt.
Add flour mixture, a little at a time, to the butter and sugar mixture, stirring to form dough.
Separate dough into two mounds, wrap in plastic wrap and chill in the refrigerator at least two hours.
Just before you remove the dough from the refrigerator, stir together egg whites with enough powdered sugar to make a "paint." (Around 4 teaspoons.) Add food coloring to make paints in desired colors.
Preheat oven to 400 degrees F.
Remove one mound of dough at a time and roll out on a lightly floured surface to about ¼ inch thick.
Use cookie cutters to cut out desired shapes and transfer to a baking sheet.
Use new paintbrushes to paint designs with the egg whites onto the unbaked cookies.
Bake painted cookies for 8-10 minutes, until lightly browned.
Remove from cookie sheet and let cool.