Combine flour, baking soda, baking powder, ginger, cinnamon, allspice and salt. Whisk thoroughly. Set aside. Place butter, brown sugar and sugar in bowl; beat at medium speed until creamy. Add molasses and egg; beat until well mixed. Add flour mixture; beat at low speed until well mixed. Divide dough in half, wrap in plastic wrap and refrigerate for at least 1 hour or until firm.
Preheat oven to 350°F. Line 3 half sheet pans with parchment paper. Set aside. Shape dough into ¾-inch balls. Place 2 inches apart onto prepared sheets; flatten slightly with the palm of your hand.
Bake 9-11 minutes or until puffed and centers just begin to set. Cool 1 minute on sheet; remove to cooling rack. Cool completely.
For the royal icing
Combine all royal icing ingredients except food coloring in bowl. Beat at low speed until moistened. Beat at medium speed 1-3 minutes or until slightly thickened and glossy (if too thick, add additional tablespoon water or more if needed. I like it to be the consistency of white Elmer's glue.)
Spoon ½ cup icing into shallow bowl. Then spoon a heaping tablespoon of icing into a small bowl, and add about ¼ teaspoon food coloring gel of choice. (Keep remaining icing covered with damp towel.) Use a spoon to drizzle some squiggle lines of the colored icing into the white icing. Swirl around slightly with a toothpick. Dip cookie and swirl it to make the marbled pattern. Remove cookie, tap off excess icing and place on cooling rack Let stand until cookies are set. Repeat this process with more cookies. Then make more marbled pattern icing with different colors and dip/swirl in additional cookies. You will probably have some leftover icing when you're done which you can store in an airtight container at room temperature for up to 2 weeks.