First, gather up and measure out all of the buttercream frosting ingredients.
Next, transfer the room temp butter to a large mixing bowl set in a KitchenAid stand mixer prepared with a whisk attachment. Beat the butter for 5 minutes, or until it is doubled in size, light, and creamy.If you do not have a stand mixer in your home kitchen then you can still accomplish this by hand using a blending whisk or hand mixer.
Then, drop in the vanilla extract, milk, and gradually add in the powdered sugar, ½ cup at a time, beating well between each addition.
Next, add a few drops of desired food coloring into the frosting mixture.For lighter, pastel frosting colors, use a toothpick to add a tiny amount of food coloring gradually until the desired color is reached.
Finally, beat the colored buttercream frosting mixture for another 8-10 minutes, until completely combined and a smooth consistency is reached.
Notes
To thin out the icing, add in the milk slowly and gradually.