For cupcakes Preheat oven to 350°F. Line 2 (12-count) muffin tins with paper liners. In a large mixing bowl, beat cake mix, 1 cup pureed fresh watermelon, vegetable oil and egg whites with an electric mixer. Beat in a drop or two of red food coloring. Pour batter into prepared muffin tins and bake 19 to 21 minutes or until a toothpick inserted in the middle comes out clean. Allow cupcakes to cool in tin about 10 minutes before removing them to wire racks to finish cooling. For frosting Beat butter with ¼ cup pureed watermelon and powdered sugar until blended. (Add more puree if the frosting is too thick or more sugar if it’s too thin.) Beat in a drop or two of red food coloring. Frost cooled cupcakes; store in the refrigerator.