Line a 15 x 10 x 1 inch baking pan with waxed paper. Prepare cake according to package directions. Pour batter into prepared pan. Bake at 350 degrees for 15-20 minutes or until cake springs back when lightly touched. Cool for 5 minutes. Turn cake onto a kitchen towel dusted with powdered sugar. Gently peel off waxed paper. Roll up jelly-roll style in the towel, starting with a short side. Cool on a wire rack. In a bowl, whisk the yogurt, pudding mix and food coloring if desired. Fold in whipped topping. Unroll cake; spread filling evenly over cake to within 1/2 in. of edges. Roll up. Cover and freeze. Remove from freezer 30 minutes before slicing.
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