There are a few ways to remove hair dye from white plastic, and the best method will vary depending on the type of plastic. For non-porous plastic, such as shower walls or tubs, you can use a hair dye remover or bleach. If the plastic is porous, such as a countertop, you'll need to use a stronger cleaner, like acetone.
To remove hair dye from non-porous plastic, start by applying a hair dye remover or bleach to the stained area. If you're using bleach, be sure to follow the instructions on the packaging carefully, as too much bleach can damage the plastic. Once you've applied the hair dye remover or bleach, scrub the area with a soft brush or cloth. Rinse the area with warm water and repeat the process until the hair dye is removed.
If the hair dye has stained a porous plastic surface, such as a countertop, you'll need to use a stronger cleaner, like acetone. Start by applying a small amount of acetone to a cloth and rubbing it onto the stained area. Acetone is very harsh, so be sure to use gloves and ventilate the area well. Once you've removed as much of the hair dye as possible, rinse the area with warm water.