Rainbow Galaxy Cookies

1. Cookies – Beat the softened butter and powdered sugar together until creamy. Add the eggs and vanilla and mix until combined. Add the flour and baking powder and mix just until a dough forms. Mix in the orange zest. Divide the dough into 6 portions. Leave one portion plain and knead the natural colors into the remaining portions. Chill the dough for 1 hour. Tear the different colors of dough into 1 to 2 inch pieces. Arrange the pieces together in a loose circle or cluster, alternating the colors. Gently press the pieces together until they stick in a disk shape. Do not knead the colors together. Chill the dough for 1 hour. Roll the dough out to 1/4 inch thick. Cut into desired shapes and place on a lined baking sheet about 1 inch apart. Preheat the oven to 350°F. Bake for 12 to 15 minutes, until the cookies are set and just beginning to turn lightly golden around the edges. Cool completely before icing.
2. Royal Icing – Beat the egg whites until foamy. Gradually add the powdered sugar and beat until smooth. Mix in the lemon juice. Add water a little at a time until the icing is thick but fluid enough for dipping. Place 3 to 4 tablespoons of royal icing into separate small cups for each color. Add 1 teaspoon of the corresponding natural color or color mixture to each cup and stir until evenly colored. Spoon small amounts of the colored icings over a larger bowl of white royal icing and lightly swirl them together. Do not over mix. Dip the cooled cookies into the marbled icing, lift them straight up, allow the excess to drip off, and leave them to dry completely.