In a mixing bowl, beat the unsalted butter on medium speed until creamy, about 2 minutes. Gradually add the sifted powdered sugar, mixing well after each addition until fully combined. Stir in vanilla extract, a pinch of salt, and heavy cream. Split the buttercream into three bowls, coloring one red, another blue, and leaving one plain.

Sift together almond flour and powdered sugar into a large bowl. In a stand mixer, whisk the egg whites until foamy, then gradually add granulated sugar, whisking until medium peaks form, about 4-5 minutes. Gently fold in sifted dry ingredients until glossy.

Line two baking sheets with parchment paper. Transfer macaron batter into a piping bag and pipe 1.5-inch circles. Tap sheets to release air bubbles, then let rest for 30-60 minutes until dry.

Preheat oven to 275°F. Bake macarons for 12-14 minutes, rotating sheets halfway through. Transfer to wire rack to cool completely.

Match cooled shells into pairs. Pipe a swirl of buttercream onto one shell, place the second shell on top and press gently to create a sandwich.