Preheat your oven to 350°F (175°C).
Grease a 9x13-inch baking pan with baking spray and line with parchment paper; spray the parchment with baking spray.
Beat the softened butter in a stand mixer fitted with a paddle attachment on medium speed until creamy, about 30 seconds.
Gradually add the white sugar and beat until light and fluffy, 2 to 3 minutes.
Add eggs one at a time, beating just until incorporated after each addition. Add vanilla extract and beat until combined.
In a medium bowl, whisk together the flour, baking powder, and salt.
Add the flour mixture to the butter mixture alternately with milk, beginning and ending with the flour mixture, beating on low speed just until combined after each addition.
Divide the batter equally between 6 small bowls.
Add one to two drops of food coloring to each bowl, tinting one bowl red or pink, one orange, one yellow, one green
