The tub stays the same color then? And the shower walls (the "surround", the paneling, the enclosure) change.

If you want to change the color of the tub that's gonna be a whole other deal.

Consider wallpaper. Easy to put on and looks good -- lots of nifty designs and it's always been popular. You can get some of the flocked stuff, maybe red or purple on shiny mirror-finish vinyl, and the tub enclosure will look just like it belongs in a...well, maybe wallpaper isn't the best idea, especially if the preacher comes visiting.