"the square of light gold-chartreuse-colored grass surrounding the millstone fountain is actually Golden sweet flag or Acorus.
It's growing in a very boggy situation and loves it. Consistent look 12 months a year if you keep it wet enough."
It was not variegated liriope (more about variegated lilyturf here) as I said in a previous post..I was playing too loose and fast with the facts...and my vision...! Liriope IS an alternative to getting a similar, though less refined and less costly, look in a drier location where Sweet Flag wouldn't work.
FYI, One issue I've had with growing Golden Sweet Flag was its tendency to revert to green over time and suffering brown tips when I didn't provide it enough moisture. A small price for its golden glow however.
Either way, John's design was spot on and I am happy to correct the record! Thanks John!