The concrete is not acid washed. It is simply Rock Salt with a color hardener applied. The concrete company the PB used is
http://destinconcrete.com/destinconcrete_colorchart.html
They had color charts we looked at. I am told the actual color name you choose can be meaningless as colors are always updating and sometimes the name applies to different colors...very comforting. So we chose to go visit with concrete sub and review color. sure enough, we picked a color simply called "sand." it is probably closer to a color between the Sun Buff and Sand Buff on their color chart.
We did not want to go darker since darker mean hotter. This color gives us just enough for our liking to distinguish from regular concrete while still being easier on the toes we imagine.