I mixed the grout. It's not the beginning or the end -- the whole
area was done at the same time. I sealed the grout, although I am
beginning to wonder if I could have not sealed it adequately. I guess
my only concern is if somehow water could be leaking behind the wall
to that area and is reflected in the darkening of the grout lines.
But they don't feel wet to the touch, and I'm not sure how water could
get to them through the greenboard, mastic and tile.