In a mixing bowl, beat the softened butter until creamy. Gradually add the powdered sugar, one cup at a time, mixing well after each addition. Stir in the salt and vanilla extract. Pour in 2 tablespoons of heavy whipping cream and beat the mixture on medium-high speed until smooth. you can add more cream to reach your desired consistency.
Divide the frosting evenly into three separate bowls. Using food coloring, tint one bowl pink, another blue, and the third purple. Mix each bowl until the colors are uniform.
Lay out a piece of plastic wrap and spoon one color of frosting in the center. Roll it up tightly into a log, pushing out any air bubbles, and twist the ends to seal. Repeat this process with the other two colors. Snip off one end of each frosting log and place them side by side into a large pastry bag fitted with a star tip.
Cut a small hole into the center of each cupcake and scoop out a bit of cake to create a cavity. Fill the hole with sprinkles, then replace the piece of cupcake you removed.
Squeeze the pastry bag to pipe the tri-colored frosting onto each cupcake, creating a beautiful swirl pattern. If you like, sprinkle a few more sprinkles on top.