Preheat the oven to 350 F. In a medium bowl, whisk together flour, salt, and baking soda. In a large bowl, mix butter with sugar until fluffy. Add in the egg and vanilla extract, and mix until smooth.
Add in the flour mixture, and mix until it is fully combined. Divide the cookie dough between two bowls. Mix one with orange food coloring and one with purple.
Take a small amount of each cookie dough, and roll together into balls. Place onto a large ungreased baking sheet at least 2-inches apart. Bake for 10-12 minutes.
