How do you remove black stains from shower floor I think it comes from hair dye?

Try using Comet. It is a powder cleaner that comes in a green circular container. Get the shower floor sightly damp and sprinkle the Comet on the stain. Let it sit for a few minutes and then scrub the Comet thoroughly on the stain with a wash cloth or dish scrubber. Rinse away. You might have to repeat it a few times to remove hair dye.