I'm a firm believer in never grouting a tile project without first testing the grout and showing the client. This is such an important step it should in fact be done well before the installation of the backer board and if you're really picky before even the plumber shows up. There are many reasons for this and I'll cover some of the thought process we use to design and build our custom showers.
All tile is different. Different textures, different edge details, different thickness and on and on. Grout can act differently with these various tile choices. Until you see a grout sample board you are hoping the colour on the bag or the colour on the grout wheel is in fact the colour it should be, or will be once grouted. So many times it's not.
Your installer might like using more water at clean up time - this can lighten a grout colour.
Your tile might have an eased edge - this can make the grout joint look twice the size once grouted.
You might like a rough looking grout joint - your installer might take great care making it smooth.
Your grout might scratch the tile
Here is a look at three grout sample boards we recently prepared for our clients to sign off on. As it turns out I didn't like any of them, but more importantly neither did my clients! Back to the drawing board, or should I say back to the grout board....
You can see here these sample boards do not need to be very fancy. Two prepared on a scrap of backer board and one on plywood. The trick is to keep the factory edges in the center and to use the desired grout spacing.
This "Raven" grout from Laticrete is one of my favourites. I told my client it would be perfect - I was wrong. It's to dark. I picked up the lighter grey colour and will make a new test board. If this colour is to light I might blend the two powders and make a custom colour.
A little to dark I think. The lady of the house wants more of a colour match. Light grey is my favourite colour and if this my shower I would use this grout. But it's not and she does not like it. I'm going to try Laticrete's white grout since it is a little off white it might be a better match.
To yellow. I hate it.
I have not kept track of the rejection rate of my grout boards with clients but would have to say it is easily 1-5 people hate the mock up or grout test board. That is a pretty high number to leave it to chance. If your looking for perfection make sure you always prepare a grout sample board.