How to get rid of sheet dye on my mattress?

So I'm getting ready to move out of my apartment complex, and the mattress isn't mine. I bought black sheets a whlie ago, WASHED THEM TWICE before putting on my bed, and now the 'dye' or whatever has bled onto the matress, does anyone know how to get rid of it?

that's really kinda gross, haha, but, I would suggest doing a quick scrub down with soap and water and then put it sideways up against the wall to dry. Or, just flip the matress and leave, haha.

maybe you could buy a new mattress and noone will notice! no just kidding! yeah scrub it down so hard that you fingers hurt!! the people that own the apartment might not even notice or even care!!