I have heard this comment about grout colours before and some just say to pick a shade or two darker to compensate. What about contacting those brands and asking them?
Who knows, maybe there’s something inherent in some tap waters that commonly can skew colour consistencies. Waters are different everywhere for a variety of reasons. If it’s well water, there are minerals like manganese and sulphur that I can see as possible tinting culprits. How about trying distilled water next time?
You cant go wrong with the TEC grouts. Its pretty much all I use, but I have used others. TEC’s Accucolor XT grout is a good choice if staining and mold are a concern. Crack grout in samples is common, as the samples get beat up pretty good. If you use the right grout and install it properly, it will not crack. TEC’s caulks in my experience are typically a little darker than their grout conterparts of the same color. I find that sometimes, a shade lighter caulk matches the grout color better.