What brand and type? Many modern grouts preclude the use of bleach.

we have used CLR, standard shower cleaner, etc. Didn't know it could be a problem. Tiler (who has been tiling 30 years) never said anything.

What brand and type of grout.

I have no idea. Was shown colors and chose the white one. Will check with tiler. thanks.

Can bleach color-change grout?

It could. Depends on the components in the grout.

The grout in it's entirety could be discolored, or the bleach could be removing a color component, leaving the "yellow" component untouched.

Chlorine bleach is not a good choice for cleaning grout.

Cleaners like Comet and Ajax can have chlorine bleach components.

Epoxy-based light colored grouts can yellow over time. It's a natural occurrence within the epoxy matrix. Some "white" epoxies have non-yellowing components to minimize yellowing to the eye. Some epoxy derivatives are non-yellowing due to them not being conventional epoxies.

More grout info, just because I have a little coffee left in my cup:

I recommend staying away from acids when cleaning, even acetic acid (vinegar). It can dissolve components in cementitious grouts.Your previously smooth dirty grout is now clean, but has a sandpaper texture. That texture will now hold soap/shampoo runoff, and your shower grout will dirty faster than before.

Non-bleach oxygenating cleaners like OxiClean can work. But do not combine them with vinegar (before or after). Nasty gasses can occur when mixing cleaning products.

Most grout manufacturers recommend pH neutral cleaners, some manufacturers even offer a specific one within their product line.

For mold/mildew removal, don't use bleach. Due to its polarity, it is a superficial sanitizer only. I usually recommend something like Concorbium. The cleaning and sanitizing components of Concorbium will actually penetrate into the grout.

Stains? If your grout is long gone color wise, if it is old, stained, blotchy, pretty much wrecked appearance-wise...then clean it, sanitize it, whatever you want. Then often times it's best to use a grout colorant over the ruined grout. Not a grout "stain" (penetrating colorant), but a grout colorant (surface applied film). Many of the grout colorants are epoxy based, it'll be like putting a near bullet-proof film coating over your old nasty grout. They can be tedious to apply. But they are durable and work well.