Szare mydło - Laundry soap
"Szare mydło" has nothing to do with any color... It is actually pale yellow or creamy white. In times when laundry detergent (proszek do prania) was not available yet the laundry soap (szare mydło) was used very commonly. It is called "szare", because in contrast to fancy, colorful, and fragrant soap for personal use (mydło toaletowe) it is very basic, plain (szare), and most likely not as harmful as other types of soap.