Preheat your oven to 375 degrees F.
In a large mixing bowl, combine the sugar cookie mix and flour.
Add in the butter and egg and stir until the dough forms.
Sprinkle a small amount of flour onto a clean counter top space or a baking mat.
Dust your rolling pin with additional flour.
Roll the dough out to about 1/4 inch thickness.
Place the dough two inches apart on your baking sheet.
Bake for 5-7 minutes.
Let the cookies cool on the baking sheet for 1-2 minutes before moving them to a cooling rack to completely cool.
To make the icing, add the egg white to a medium mixing bowl and beat until frothy.
Add in the vanilla or almond extract and powdered sugar. Mix until smooth. The icing should be thin.
Create the marble icing by transferring about 1/2 cup of icing to a small shallow dish.
Add a drop of green food coloring to one side of the dish and a drop of red to the other side.
Set each cookie onto parchment paper to dry.
Continue this process with each cookie until the icing gets low. You may need to add another drop of each color of food coloring if the colors start to fade.