Place paper baking cups in muffin pan. Combine crumbs, nuts and butter; press mixture evenly inside baking cups. Bake 8-10 minutes; cool.
In a mixing bowl combine juice, sugar and egg white. Beat at high speed until soft peaks form (about 10 minutes). Add food coloring. Gently fold in sour cream. Spoon into tart crusts; freeze. Remove baking cups to serve
Yield: 12 tarts
Lemon or Lime Tarts: Substitute 1/4 cup frozen concentrated lemonade and yellow coloring or 1/4 cup frozen concentrated limeade and green coloring for orange juice and orange coloring.