The best way to remove a black hair dye stain from a bathtub is by mixing one part hydrogen peroxide or bleach with three parts water, then applying the mixture to the stain. The solution should sit on the stain for 10 to 15 seconds before being scrubbed away.
The bathroom should be well ventilated before applying bleach to the bathtub. Bleach and hydrogen peroxide work best on light-colored, porcelain bathtubs, but if the bathtub is a darker color, then an alternative cleaning solution should be used because bleach or hydrogen peroxide could stain a darker bathtub.
Nail polish remover, vinegar or a Magic Eraser sponge by Mr. Clean are some alternatives to bleach and hydrogen peroxide. Nail polish remover that has high levels of acetone works best. The stain can be removed by soaking a cotton ball with nail polish remover and then rubbing. The area should then be rinsed with water to remove any remaining nail polish remover or dye.
If using vinegar, a clean cloth should be soaked with white vinegar and then placed on top of the stain for at least an hour. Vinegar works best when the stain is fresh.
Lastly, when using a Magic Eraser sponge by Mr. Clean, the Magic Eraser sponge should be first dampened with water before being used to scrub the stain away.