Apparently this works

Fortunately, it's quite easy to remove soap scum stains from marble – just add half a cup of ammonia to a gallon of water and wipe the surfaces clean. Be careful not to use too much ammonia, though, as it may dull the marble surface.

Welcome to the world of marble.

Thank you, Patricia, I will try that!

My daughter spilled blue hair dye on her bathroom marble counter. It looked like it was a deep stain. I put a poultice of baking soda. Covered it with Saran Wrap over night and to my amazement it lifted the stain completely out. Shocking.