Any firberglass/acrylic pan is going to get dingy after a while, even with regular cleaning. Have you considered setting a darker coloured pan? Or using a tiled shower base with darker tile and small sealed dark grout lines?
In any case, never store your bottles, especially metal cans, on the shower floor. There are numerous shower shelf/basket products that attach to the walls of the shower with suction cups so that you don't stain the floor or create a nice spot underneath the bottles for mildew to form.