Mix your food coloring hair dye in a plastic bottle with a tight-fitting lid. Place shampoo in the bottle, then drop in six drops of coloring for every ounce of shampoo. The amount of mixture depends on the length and thickness of your hair.
Place the lid on the plastic bottle, then shake the bottle vigorously to blend the dye and the shampoo. If your shampoo is thick, remove the lid and add up to 1 tbsp. water. Replace the lid and shake the shampoo a final time. Shake the bottle for one to two minutes to ensure the color is evenly distributed.
Put on a pair of rubber or latex gloves, and drape an old towel over your shoulders. Wear old clothes, because any food coloring spills will be very difficult to remove. Smart a thin coating of petroleum jelly around your hairline and ears to prevent the dye from staining your skin.
Dampen your hair, then massage the dye mixture into your hair. Begin at the roots and work the mixture to the ends of your hair.
Place a plastic shower cap over your hair. Be sure your hair is entirely covered by the plastic.
Check the color of your hair after 30 to 40 minutes, then pull a few strands of hair from the shower cap. Rinse the strands in warm water, then dry the strands with a towel. If the color isn't as dark as you would like, check every 30 minutes until the desired color is reached. The lighter your natural hair color, the faster your hair will absorb the color from the food coloring.
Rinse the food coloring mixture from your hair with warm water. Allow your hair to air dry, or dry your hair using a soft towel or a blow dryer.
Wait four or five days before washing your hair to allow time for the color to set.
Food coloring hair dye can be applied in the shower. However, be sure to rinse the food dye immediately to avoid staining your tub or shower.
Test the food coloring on your skin three to four days before using the dye to color your hair. If you notice redness, irritation, or any type of allergic reaction, don't use the food coloring on your hair.