In a large bowl, cream butter and sugar until light and fluffy. Beat in eggs, milk and vanilla. Combine flour, oats, baking powder and salt; gradually add to creamed mixture. Fold in toffee bits and pecans.
Spread into a greased 9-in. square baking pan. Bake at 350° until a toothpick inserted in center comes out clean, 20-24 minutes. Cool on a wire rack. Add food coloring to frosting; spread over bars. Cut into diamond shapes.