Add butter and shortening in a large mixing bowl and mix until smooth.
Add vanilla extract and mix until just combined.
Add powdered sugar (½ cup at a time), while continuing to mix. Add milk (1 tablespoon at a time), while continuing to mix until you reach the desired consistency.
Add a generous amount of red food coloring (about 3 deep squirts) and mix until evenly distributed. The frosting will mostly likely be looking like a dark shade of pink.
Spoon out ½ cup icing and transfer to a bowl.
Add a 1 more squirt of red coloring until the color is even brighter and more vibrant.
Heat in microwave for about 15 seconds or until frosting is runny.
Mix with a spoon and you will notice this runny icing is bright red now.
Add this runny frosting into the original bowl of icing and mix until the red color is evenly distributed.
Cover and chill in fridge for at least 3 days but preferably 5 days to allow the shade to truly deepen and develop further. This is a crucial step and cannot be skipped.
When you are ready to use this icing, remove bowl of icing from fridge and let it come to room temperature.
Then, fill a piping bag and start piping your cake and cupcakes.