In a large saucepan, combine rhubarb and 3/4 cup sugar; let stand for 15 minutes. Bring to a boil. Reduce heat; simmer, uncovered, for 10 minutes or until thickened, stirring frequently. Remove from the heat; cool completely.
Stir in the yogurt, orange juice, remaining sugar and food coloring if desired. Cover and refrigerate overnight.
Freeze in an ice cream freezer according to manufacturer's directions. Transfer to a freezer container; freeze for 2-4 hours before serving.