Recast Graph Colors

What does yellow represent after generating a navmesh from a Recast Graph? I assume it means a disconnected (but walkable) island, but I’d like to have that confirmed.

That is correct.
A different color represents a different area. An area is a connected component of the graph (i.e disconnected but walkable island).
That special yellow color is area 255 which is assigned to “small” areas to avoid lots of small areas using up all the available area IDs (only 256 available). It can be controlled using the A* Inspector -> Settings -> Min Area Size field.

Thanks – is there a way to prevent these “small” areas from being added? In the example screenshot they are occurring on top of tables, etc. I would prefer there is no pathfinding data on such surfaces.

At the moment, that is not implemented. I have it on my ToDo list.