You didn t indicate whether the tile is a glazed ceramic tile or an unglazed ceramic tile or whether either of those types of ceramic tile were porcelain body tiles.
Discoloured ceramic tiles.
I was inspired by the way you referenced installing pictures and did the same for myself.
Cleaning your ceramic tiles.
To give your tiles a deep clean take a bucket of hot water and add a couple of drops of mild dish.
The ctef certified tile installer cti program is the only third party assessment of installer skill and knowledge which is recognized by the tile industry.
Someone mentioned they are ceramic and absorb water.
Step 5 prevent discoloration from reoccuring.
The ceramic tile education foundation ctef provides education and installer certification for professionals working in the ceramic tile and stone industry.
Dirty stained grout can make an otherwise clean tiled area look filthy.
Removing the stains without replacing the grout requires some effort but is less intensive.
While it may seem obvious regularly cleaning your bathroom floors is the most effective way to prevent tile discoloration.
Likely not so coincidentally there is a 4 strip of adhesive vapor barrier along the bottom row to the shower pan that correlate with the discolored tiles.
How to clean discolored grout.
After all the tile based discoloration has been successfully removed use a water soaked sponge or mop to get rid of any remaining traces of your solution.