If by bottom you mean the white sole, well, that picture I think it was after a cleaning I made for most of my designer footwear, I followed a GQ tip for cleaning white on shoes and it worked wonders, well it was some sort of a mix between the GQ tip and something I read online, I firstly dissolved baking soda in warm water and with a used toothbrush started cleaning the white or bright coloured sole (the Fendi shoes with yellow soles too) and then I took a little toothpaste and brushed all over, then finally I wiped with a wet cloth and voilá, it worked wonders honestly.Great styles!
Wow the bottom of your shoes is so clean!
Also from that day onwards I've been spraying the soles with a water/stain repelent I bought at nine west, it's some sort of teflon layer that helps for stains to be easily removable. (That works perfectly with the latest pair of Fendi sneakers I got since 80% of the sneaker is fabric, so go figure)