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Transfer plain white frosting to a mixing bowl using a spatula or spoon. You may want to reserve a small amount of white frosting in case you want to lighten the color of the frosting later. Natural food coloring is better for you than artificial food coloring. You can use all one color, or use multiple colors. Mix a few drops of food coloring into the frosting by hand or with an electric mixer. Keep in mind that 100 drops of food coloring equals about 1 teaspoon (5 mL).  Make pink frosting by adding 11 drops of red and 3 drops of yellow. Make lavender frosting by adding 5 drops of blue and 5 drops of red. Make mint green frosting by adding 3 drops of blue and 3 drops of green. If the color is too dark, add more plain white frosting. If the color isn’t dark enough, add another drop or two of food coloring. Then, mix the frosting thoroughly. Continue adjusting the color until you get the desired result.

Summary:
Empty white frosting into a mixing bowl. Mix food coloring into the frosting. Adjust the color, if needed.