As long as there's no soiling or coating on the surface there's a product I use for stains when it works it's fast and it's incredible. A few hrs. Or 24hrs.
It a hydrogen peroxide base. It's a hair product that women use for lightening their hair.
I buy the storebrand by the gallon at a beauty salon supply store.
L'Oreal 40 volume, regulator oxidizer. Link below.
2 two weeks ago, upstairs balcony brand-new printed Black and white concrete tiles 50sqft. Covered with sawdust from the tree cutters. It look like permanent yellowing stain the concrete. I covered it with this product in one hour. Return the next day rinse it off with a garden hose no scrubbing at all. I made $1000.