Mapei Silver grey darker than expected - Tile Advice

[davisc02]

Not sure if anyone can answer.

My mate and I both had kitchen floors layed by the same guy.

Me = porcelain tiles with Mapei silver grey grout
My Mate = quartz tiles with Mapei silver grey grout
My grout is as expected and after 8 months still a lovely silver grey
My mates went dark immediately and never went light even after drying. He regrouted a different batch of mapei silver 6 months later and still dark grey

Cannot figure it out, any idea?
Thanks

 

[davisc02]

Mine is the darker picture but lighter grout his is lighter picture with darker grout, both mapei silver grey

 

[Diane Teale]

That's strange. I have no idea but maybe it has something to do with the different tiles you both used. It may appear that way because your tile is darker and his, is lighter.