In a medium bowl, beat butter, granulated sugar, and light brown sugar together until light and fluffy.

Add egg, cream of tartar, baking soda, salt, and vanilla and beat until combined.

Gradually add in the flour, beating until combined. Divide the dough into four sections.

Dye the sections of dough orange, teal, pink, and purple by kneading a few drops of gel food coloring into each section. Aim to have one color per dough section.

Wrap each section of dough in plastic wrap and chill for 15 minutes.

Preheat the oven to 375 F. Line two baking sheets with parchment paper.

Take some pieces of each color of dough and roll into a ball. Aim to have a 1-inch ball, but they can be a little bigger. Place the dough balls onto the prepared baking sheet, a couple inches apart.

Chill dough balls for 15 minutes before baking.

Bake for 9-12 minutes or until the edges are just starting to brown.

Let cookies cool for two minutes on the baking sheet before transferring to a wire rack to cool completely.

In a small bowl, whisk together the sugar and meringue powder.

Add warm water and beat until smooth.

Beat on high speed until the icing is smooth and glossy and reaches stiff peaks.

Stir in a few drops of balck gel food coloring.

Transfer to a piping bag.

Pipe stitches along the cookies where the different colors come together.