Beat the butter and sugar with an electric mixer until pale and fluffy. Add the vanilla extract and eggs one at a time, mixing with each addition.
In a separate bowl, combine the flour, baking soda and salt. Add this to the batter in 2 additions, alternating with the buttermilk.
Divide the batter into 3 bowls and dye them pink, blue and yellow.
Pour the batter into 3 greased and floured 8-inch round cake pans. Bake at 350F for 40 minutes, or until a skewer inserted into the middle comes out clean. Cool in the pans for 10 minutes, then transfer to a wire rack and cool completely.