where did you find the dark grey sand for in between? California only sells grey ( more brown) and tan. we've been looking for dark grey polymeric sand for our charcoal flagstone.
We used a polymeric sand for these joints. I believe that the color was called slate grey by Gator Max. This was a sand set installation. If you are mud setting the stone in place, then we use a grey mortar mix, and we add charcoal color dye into the mortar mix.
Matthew Giampietro Garden Design