Preheat oven to 325°. Place a greased 9-in. springform pan on a double thickness of heavy-duty foil (about 18 in. square). Wrap foil securely around pan. Place on a baking sheet., In a small bowl, mix flour, sugar and zest; cut in butter until crumbly. Press onto bottom of prepared pan. Bake until edges are lightly browned, 25-30 minutes. Cool on a wire rack., In a large bowl, beat cream cheese and sugar until smooth. Beat in flour and vanilla. Add eggs; beat on low speed just until blended. Divide batter into thirds. To 1 portion, add lime juice, lime zest and green food coloring. Pour batter over crust., Place springform pan in a larger baking pan; add 1 in. of hot water to larger pan. Bake until center is just set and top appears dull, about 25 minutes., Meanwhile, to another portion of batter, add lemon juice, lemon zest and 3 drops yellow food coloring. Carefully remove pan from oven. Gently spoon over lime layer. Return to oven; bake until center is just set and top appears dull, about 25 minutes., To remaining batter, add orange juice, orange zest, red food coloring and remaining 3 drops yellow food coloring. Carefully remove pan from oven. Gently spoon over lemon layer., Return to oven; bake until center is just set and top appears dull, 30-35 minutes. Carefully remove pan from oven., In a small bowl, whisk topping ingredients. Gently spoon over cheesecake in small dollops; spread carefully. Return to oven; bake 5 minutes., Remove springform pan from water bath. Cool cheesecake on a wire rack 10 minutes. Loosen sides from pan with a knife; remove foil. Cool 1 hour longer. Refrigerate overnight, covering when completely cooled. Remove rim from pan. If desired, top with orange, lime and lemon slices. Refrigerate leftovers.