I decided the color transitions were too abrupt and spent Saturday tearing all the rock walls out (one step back).
The next step forward was changing to one strand of the variegated thread and one strand of solid gray, zigging and zagging irregularly for a more nuanced effect, much like the limestone walls themselves:
Adding the lettering was another do/undo/redo process. Fortunately, I revised the plan from an earlier post (much as I repeatedly revise recipes), choosing to stamp the lettering using a V-Clear water-erasable pen instead of the "permanent" ink markers. If a letter was misplaced, it was easily removed with a bit of damp toweling, then re-inked. I didn't go for perfect placement, however. I was especially pleased that the Stepping Stones variegated floss by Crescent Colours (one of three brands I purchased in Williamsburg) was far more subtle than the thread in the rock walls since the lettering could only be done with a single strand.
Here's the top half so far ...
and the bottom half ...
With the rock walls and most of the lettering done, I'm now starting to experiment with how to stitch the trees and grasses ... no doubt this too will change: