In a mixing bowl, combine margarine, egg white, and vanilla extract. In anther mixing bowl, combine flour, sugar, and baking powder. Mix wet ingredients with dry ingredients just until moistened. Divide dough into 3 equal portions. Tint 1 portion with red food coloring and another portion with blue food coloring. Mix throughly to get a uniform color. Untinted dough represents white. Form each portion into long bars. Wrap each bar in waxed paper. Refrigerate until easy to handle. Remove wax paper and stack bars on top of each other in the desired color arrangement. Wrap entire bars in waxed paper again and chill until firm. Preheat oven to 350. Slice bars into 1 cm thick. Place on baking sheet. Bake for dozen minutes.