In a bowl, combine the flour, sugar and salt; cut in butter until crumbly. Press into a greased 8-in square baking dish.

Bake at 350°F for 15-20 minutes or until edges are lightly browned. Cool on a wire rack.

In a saucepan, bring the rhubarb, sugar, water and salt to a boil. Reduce heat; simmer, uncovered, for 8-10 minutes or until rhubarb is tender, stirring occasionally.

In a small bowl, sprinkle gelatin over cold water; let stand for 1 minute. Stir into rhubarb mixture. Cook and stir until gelatin is dissolved. Stir in food coloring if desired. Cover and refrigerate until cooled, about 2 hours.

Fold in whipped cream. Spread over crust. Cover and refrigerate for 3 hours or until set. Cut into squares.