Mix butter and sugars for four minutes with whip attachment.
Add eggs one at a time to butter mixture. Then add vanilla.
Put all dry ingredients in a bowl.
Change out the whip attachment for the paddle attachment.
Gradually add flour mixture to cookie dough. This dough is stiff. Make sure to add all the flour.
Divide the dough into six equal parts.
Mix 3 drops of color into each of the dough balls. Mix until color is well incorporated.
Once color is mixed in, wrap the dough in parchment paper.
Place in the refrigerator for 2 hours or overnight.
When you are ready to make the cookies, preheat oven to 350°.
Roll out each color into a long rectangle, 4 - 5 inches wide and 18-24 long.
Stack each color on top of each other. The color order, starting from the bottom, is purple, blue, green, yellow, orange and red on top.
Trim the edges and then cut across the rectangle.
Bend the cookie dough into a rainbow shape and place on a greased cookie sheet for a large cookie. Cut in half for a smaller cookie.
Use the back of a spatula to push cookie flat.
Bake for 14 minutes for big cookies and 10 minutes for smaller cookies.