1.make a basic sugar cookie, but don't bake it.
2.obtain a paintbrush. and have a cup of water near by.
3.paint the cutouts of your cookie with water.
4.then dip your paintbrush into the water, then into the food coloring, and back into the water.
5.paint the cookie cutout with paintbrush, repeat pattern with all colors.
6.before putting into the oven, brush over lines between colors with water to get them to bleed a little bit.
7.bake as normal.
(you might have to cut your coloring with some water, because it'll be pretty bright. thats why mine looks a little intense.)