In a stand mixer with the paddle attachment, cream the cold butter until smooth.
Slowly add in four cups of powdered sugar and vanilla extract until combined.
Test the buttercream stickiness by grabbing a small amount and rolling it between your thumb and pointer finger. If the frosting resembles playdough, move to the next step. If it is sticky, add more powdered sugar, up to two more cups if needed.
Add the gel food coloring to the mixing bowl and mix until incorporated.