Darkening of granite tile counter after installation

I've recently been working on a counter tiling project at a friend's house. We used a light grey/white/black speckled granite tile for the field. Our question is this: as the tile has been sitting after installation for the last two days, the tile has darkened considerably in color, much like the color it darkened to after coming off the wet saw. Did we do something wrong in installation, or is this absorption of moisture from the thinset a typical occurance with light colored stone that will clear up with time as the stone dries out? The adhesive used was white. We haven't done any grouting yet, and I seem to be finding conflicting advice online as to whether or not we've really messed up this project. Any advice you can provide would be appreciated!

 

Robert:

If you can't use white thin set to set stone, then what else could you use??!...

It may take a few weeks, but it will go away. If you don't grout it will dry a little faster, but not by much.

Of course, you do not want to use colored grout, right?...

Ciao and good luck,

Mauri z io Bertoli