Hi Fran, I would say it would be either peel and stick tile decals or the peel and stick tiles.
A couple days ago, here on Hometalk I think, was an article abt using the peel & stick tiles to make a kitchen backsplash, which looked really nice. I looked up a few kinds & some said the could not be used in showers so it would be good to check the mfr's instructions before buying.
Nothing that will hold up for a long time. You can use the epoxy paint kits made for that sold at home depot. Step by step instructions are in the kit. If careful will look good for several years.
How about painting it? I wouldn't use peel and stick tiles, most say they are not for shower use. https://www.hometalk.com/41518519/how-to-paint-over-that-ugly-bathroom-tile
You could paint it! I painted our entry way tile: https://www.aratariathome.com/blog/painted-tile-tutorial-entry-way-makeover-part-2