In the large mixing bowl beat the butter on low for a minute or so until smooth.
Add sifted powdered sugar ½ cup at the time and beat slowly until fully combined.
Add vanilla extract and pinch of salt. Mix well with spatula.
Split cream between 3 bowls and add red food coloring into one bowl and blue into second.
Place each color of the buttercream in a separate pipping bag.
Layout a sheet of plastic wrap and pipe a straight line of each cream color next to each other on the plastic.
Roll up the plastic gently, then cut the tip and place into pipping bag with Wilton 4B Pipping tip.
Pipe the buttercream on one macaron shell and place the other shell on top, pressing down slightly. You need to make sure shells stick together.
Place filled macarons into airtight container and let them mature in the fridge for 12 hours or overnight.