Food coloring can be permanent on clothes and makes for a good way to dye the clothes.
However if you want to remove the food coloring from clothes you can pour some hydrogen peroxide in a bucket and add a bit of water and then soak the clothes in the bucket of water and hydrogen peroxide.
And then stir the clothes up in the bucket and then blot or scrub the food coloring out of the clothes.
Or add some hydrogen peroxide directly to the food coloring spot and allow it to sit for around 10 to 30 minutes and then take a damp cloth or sponge and blot the food coloring.
You can also add some vinegar and baking soda to the food coloring stain and then allow it to sit for a few minutes and the food coloring should come out.
Once food coloring is dried it can be hard to come out just by washing it but by using some baking soda and vinegar or some hydrogen peroxide the food coloring will usually come out of the clothing.
You might also need to soak the clothes overnight in some hydrogen peroxide and water or vinegar, baking soda and water or in some stain remover.