Preheat the oven to 350 F. In a medium bowl, whisk together flour, salt, and baking soda. In a large bowl, mix together butter, peanut butter, granulated sugar and brown sugar until smooth.
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 into two bowls.
Mix green food coloring into one bowl and blue into the other. Take a small amount of each cookie dough and roll together into a ball. Place onto a large ungreased baking sheet at least 2-inches apart. Bake for 10-12 minutes.