Preheat oven to 325°F. Prepare pans with vegetable pan spray.
In medium bowl, sift together flour, baking powder and salt; set aside. In large bowl, beat butter and sugar with electric mixer until light and fluffy. Add egg whites one at a time, beating well after each addition. Add vanilla and beat well. Add flour mixture to butter mixture alternately with milk; beat until just combined. If desired, tint portions of cake batter with icing color. Divide evenly into prepared pans.
Bake 17-20 minutes or until toothpick inserted in center of cake comes out clean. Cool 5 minutes in pan on cooling grid; remove and cool completely before icing.