In your stand mixer, whip together the butter and shortening until combined.
Add the vanilla, salt, and powdered sugar and mix until incorporated.
Scrape the sides of the bowl and add the heavy cream. Whip until smooth.
If the frosting is too thick, add 1 Tbsp more cream until you reach your desired consistency.
Whip on high for 2-3 minutes or until light and fluffy.
Reserve half the frosting for the brown and set aside.
Add a SMALL amount of blue gel coloring to the remaining white and whip until combined.
Decorating the 6 light blue cupcakes.
Add more gel coloring until you get a deep dark turquoise blue and whip until combined. Let the color sit in the frosting for 5-10 minutes before piping, it will turn deep and dark in color.