White stain after cleaning with public restroom soap and water, how can I get rid of it?

A couple months ago I was eating in an airport and got some sauce on my shoe. I went into the restroom and cleaned the sauce off with some soapy water and a paper towel and it left this white stain. When I got home I tried cleaning again with some dish soap and more water, and it’s not going away. How can I get rid of it or perhaps make it so that my other shoe matches it? Perhaps the water/soap in the airport had some sort of bleach/chlorine in it that caused this?