First, thanks for the replies.
Second, I should have been clearer in that the heightfield was plugged into both the Compute Terrain and Compute Normal nodes in the original image. I just did not include it in the image or tgc.
I tried the Texture XYZ but it did not link the color to the fake stone boundaries. Nor did any combination of Compute Terrain, Compute Normal, or Texture XYZ except when the Compute Normal is plugged into both the fake stones and the surface layer. However, that dual-Compute-Normal result gives pyramidal stones, not rounded, so it is not an answer either.
The only way I can get this to work is by NOT bothering to color the fake stones at all (since the coloring does not align), but plugging uncolored stones into a surface layer's main input and coloring that surface layer separately (which colors the entire planet), then using a Merge node with Highest (Raise) to merge the fake stones into my base Compute Terrain colored landscape. My hunch is that while this solution works, it would not allow for particular, nuanced coloration on the stones (such as if you wanted to color the stones on one of their sides, such as north moss growing).
Could anyone explain why the Compute Terrain does not work in aligning colors (when the Merge node is not used, as in the original examples at top), or why the Compute Normal node does align color but generates pyramidal, non-rounded stones? The more I understand the workings of how, why, and why not of TG, the better I'll be able to troubleshoot issues myself before they arise.
Thanks,
Matt