Bake cookies according to package directions. Cool completely. In a medium bowl, combine 2 cups sugar and salt; stir in 3 Tbsp water and juice. Stir in food coloring, a few drops at a time, to tint icing bright yellow. Using an offset spatula, spread icing on flat sides of cookies, covering them from one-eighth to almost completely. Freeze 10 minutes or until set. In a medium bowl, combine remaining 2 cups sugar, cocoa powder and 3 Tbsp water. Spread chocolate icing on un-iced portions of cookies to represent moon covering sun. Refrigerate 5 minutes or until icing is set.