Some of the brands, maybe all, have higher quality lines with special properties like true color or color fastness. I think mapei does too. It's not just that brand that happens with. I selected TEC XT and it was all washed out. I assumed he used too much water which can either cause a chalky effluorescence on the surface that then needs to be removed or the pigments can even be washed out. The pigments seem to have been washed out on mine. Other room with mapei seems to be effluorescence. It warns of this right on the mapei bag, for one. Unfortunately, installers don't seem to be aware. Cover all bases.

Good research over at John Bridge tile forum. The pros there do recommend using vinegar as a first resort to remove the chalky stuff. Stronger acid cleaners if it doesn't work. Never heard the bleaching effect mentioned here before but acids can be hard on the grout.

Did you read the thread where people are mixing their own color? Definitely test and I would beware of your tap water too.

Good luck getting the installer to cooperate.

I just want a true dark brown grout. Is that asking too much of the grout sellers???