We've had some Mapei grout installed, chosen on the basis of a Mapei sample stick. It is at least two or three shades lighter than the sample stick and has somewhat diminished the look we were going for which was to try and match the colour of the floor tile as much as possible. Tiler swears he mixed it correctly.
I found some reviews online from others who have experienced the same. Is this is a common phenomenon? It appears it might have something to do with using hard water to mix it with, instead of distilled water.
A common solution that has been proposed is to use something referred to as a stain pen or a grout shield. Has anyone come across this? Does it work?