I don't know about substrate being dry - sounds incorrect since that would not cause the pigment to flow anywhere.

Maybe it just needs more time to cure.

If you decide to redo it, the grout will come out much easier this time since it's not yet as hardened.

It could be a change in the pigments used in the grout. If you don't want to rework the grout, there's a company called This Old Grout that (for lack of a better term) has color matched dyes for grout. I used on a botched grout job and it looks great.

Here is a link that might be useful: This Old Grout

Unless you used grout from the same bag as was used originally exact matching is an iffy sort of thing.

Even if you have the rest of a bag of grout it sometimes comes out slightly off the original color.

Thanks. I tried what the grout manufacturer recommended (dig out and mist the area with water prior to applying the grout) on just a few inches as a test. It did not work. However, I tried the same batch at the other end of the shower on a two inch stretch and it dried in the exact correct color. A real mystery.

djlandkpl, This product sounds too good to be true, but I have an open mind. Was your application on a shower floor? how long has this dye been in place? and is the shower used a lot? Thanks.

Even though it is a different batch, the grout left in the mixing pan dried to a correct color.

Perhaps you are overworking the grout although that usually results in the grout being lighter.

The dye has been in place for 6 months and it looks the same as the day I put it down. It's not in a shower, just the floor. In my case I had nothing to lose. Either try it or redo the whole floor. The product colors and seals at the same time so it should be durable. I discovered the product over at the John Bridge forum.

Thanks. I will try another small test. If that doesn't work, will look the product up.

Could there be a small leak in the pan, causing the grout to dry darker? But that doesn't explain why it's not consistent throughout unless the moisture hasn't reached the entire shower pan yet?

I see you are the same poster removing grout between the wall/floor joint on another thread. Has someone used this shower without a seal on the shower floor?

I do not understand how a pan leak would affect grout color? This shower is on a mud pack on top of a PVC liner. When I cut into old grout was vary careful not to dig into mud.

Sealed it when it was new about 3 years go. but not resealed since (will fix this mistake after I straighten this all out). The shower has not been used for 2 weeks now, so all substrates should be dry. I did another test yesterday on a 3-inch section without any misting of substrate and, although it probably needs another 2 days to cure, it does still look too dark.

I would go to the John Bridge tiling forum and post your query, they are the best in North America for tiling info.

Update: I did another small test area without misting the substrate. The grout dried seriously darker than the leftover grout in the bucket and the surrounding tile.

I also called Custom Building Products, the grout manufacturer and a technical support person was kind enough to review my photos. He guesses that there is something in the subsurface (thinset or mudpack under the floor tile), such as old soap scum or body oil, that could be leaching into the grout. However, he is not sure. He also said that grout stains are available, but they are not good for shower floors.
Anyone have any ideas or experience with this type of problem?

"experience with this type of problem? "

Multiple rentals with repairs over the years.

Tincture of time.

The grout seems to accumulate enough non-removable 'dirt' to eventually become uniform.

Hi Brick. "The grout seems to accumulate enough non-removable 'dirt' to eventually become uniform." Sorry, I am not getting what you are getting at? The issue is the new grout in the repair areas cures a much darker color than it is supposed to; yet the grout left in the mixing bucket is the correct color. All this after waiting several days.

You are working it excessively when you install it most likely.

The leftover in the bucket is also likely not nearly as thin as the grout installed on the floor.

It is unlikely you worked the grout left over as much either.