Clean mold/mildew from honed travertine tile in shower
2 household chemicals come to mind both work well for killing mold spores. House hold bleach and hydrogen peroxide. Both have the possibility of changing the color, I prefer hydrogen peroxide because it doesn't smell as bad. I learned about using Hydrogen peroxide when working at a hospital for a few years they would purchase stronger than the normal store bought type and add it to water then wipe the infected areas down. Since finding this out I have used a 3% solution to remove mold from carpet and spray directly on wooden surfaces with better results than bleach and less damage (discoloration) without the smell of bleach. The store bought Hydrogen Peroxide will work with a good saturation of porous surfaces.