Preheat oven to 375°.
Prepare cake mix according to package directions, using 3/4 cup water. Let cake cool in pan; remove from pan, and cut into cubes.
Prepare pudding mix according to package directions, using 2 cups fat-free milk; chill at least 30 minutes.
Thaw cherries, reserving 1/4 cup juice. Combine cherries, juice, and food coloring.
Place half of cake cubes in a 3-quart trifle bowl. Spoon half of cherries over cake; spread 1 cup pudding over cherries, and top with half of whipped topping. Repeat layers. Garnish with chocolate curls, if desired (chocolate curls not included in analysis). Cover and chill at least 8 hours.
Look for sugar-free cake mixes alongside the regular cake mixes or in the dietetic section of the grocery store.