Grease 2, 17 x 11 pans. Line with wax paper. Grease and flour again. Mix chocolate cake mix according to package directions. Pour into pans. Bake at 350~ for 15 minutes or until tested done. Peel waxed paper off immediately. Mix yellow cake mix according to package directions. Prepare pans as above. Pour 1/2 of the batter in one pan. Color other half of the batter with the red food coloring. Bake at 350~ for 15 minutes or until tested done. Peel waxed paper out immediately. FILLING: Beat butter, cream cheese and confectioners's sugar with milk and salt inelectric mixer. Beat well until fluffy. Color with green food coloring. FROSTING: Mix butter, salt, cocoa, milk and confectioners' sugar well and whip until smooth. ASSEMBLE: Cut each layer into 4 even rectangles. You will have 16 cake rectangles. Place one layer on an attractive tray and spread with some filling. Continue until all layers are used, alternating colors, with filling between each layer. Frost sides with thin layer of chocolate frosting. Can be frozen. ----