In a large bowl using an electric mixer beat the butter until light and fluffy.

Gradually add in powdered sugar, 1 cup at a time, beating well on medium speed after each addition.

Add in heavy cream a little at a time until desired consistency is reached.

Add in vanilla and salt then mix well.

Divide frosting into 3 separate bowls. Use a few drops of fuchsia, violet, and teal to color each bowl of frosting. Stir until each color is consistent.

Spoon each frosting color into a separate piping bag that has been fitted with a closed star tip, such as the Wilton 109 or 129 tips or the Ateco 855 tip. Clip the top of the bag closed so that the frosting won't spill out.

To put together the clamshell cookies, take one vanilla wafer and pipe a single color of frosting in a circular motion around the wafer. Place a single white Sixlet toward the front of the wafer like a pearl in a clam shell. Place another vanilla wafer on the top but angle it so that the back is lower and the front is higher like an actual clam shell.