Place a saucepan filled with 1 cup of water over medium-low heat. Pour the white chocolate chips into a small, heat-safe bowl that will fit over the saucepan without touching the water. Set the bowl over the saucepan to make a double boiler, and stir the chips until they melt. Add 1 drop of the food coloring and continue to stir. After 30 seconds, add the next drop. Once the desired pink color is achieved, turn off the heat.
Put a piece of aluminum foil (about 1 square foot) on your countertop and shape into a concave curve. Place a piece of plastic wrap on top of the foil. Using a tablespoon, scoop one spoonful of the melted chocolate onto the plastic wrap and spread into the shape of a rainbow using the back of the spoon. Repeat with the remaining chocolate. Let the chocolate petals set for 10 minutes.
Gently peel the chocolate off of the plastic wrap and place on a tray lined with parchment paper until ready to use.