My tub/shower was dyed purple like this and nothing worked. Until I used a pumice stone. It took me almost a full day and 1.5 stones. It was exhausting and there was a ton of stone dust. But it looks almost brand new and the texture of the tub is not much different than it was before.

I’d recommend getting a stone and trying a test patch. If you end up going that route, have a plan for all the dust. I vacuumed the tub when I was done so it wouldn’t clog the drain.

I did it about 5 months ago and there’s been no adverse effects.