HanStone Recommends:

Option 1 – Soap & water or rubbing alcohol & water solution
Option 2 – Soak a cloth with a 50% bleach concentration. Apply to top of stain for 10 minutes. If stain persists, reapply, but do not leave on for longer than 30 minutes.
Option 3 – Apply hydrogen peroxide with a max 30% concentration. Then, rinse and wipe surface with water.