ADD 3/4 cup boiling water to raspberry gelatin mix in medium bowl; stir 2 min. until completely dissolved. Refrigerate 15 min. or until cooled. Whisk in 3/4 cup yogurt until blended. Pour into 9x5-inch loaf pan sprayed with cooking spray. Refrigerate 30 min. or until gelatin is set but not firm.
REPEAT with remaining gelatin mix flavors to make a total of 4 layers in loaf pan. Refrigerate 2 hours or until firm.