Thanks — yes, I'm still struggling to find a good way to explain the colors. The landmark is green. The blue tiles are the savings — the difference between using the landmark and not using it. I'll work on a different wording or maybe a visualization.

Changing the graph is another optimization that's commonly used. A graph of rooms is far smaller than a graph of tiles, and you can precompute paths on the small graph. The landmark heuristic can work on that graph too, although with the small examples on the page you probably wouldn't need to.