It is not your fault when tub & shower floors gray-out!
Housekeepers and homemakers have traditionally done a great job keeping rooms clean. They work hard and take pride in their job and their homes. A housekeeper knows she/he has done all she/he could do to keep the tub & shower floors clean and white, but over time the floors turn gray regardless of effort.

Gray-out is a result of simple dirt build-up AND a chemical reaction.
Gray-out is caused by the accumulation of body, tanning, soap, shampoo, and body-lotion oils in the non-skid crevices of fiberglass and acrylic tub & shower floors. Even an intensive cleaning and rinsing will still leave traces of oils in these areas. The minute amount of oil(s) will polymerize (harden into a type of plastic) and weld itself to the floor surface.