Looks good. I think the colors indicate the distance-parameter for the objectsize in the pathfinding.
Since you have quite a large grid, try to make "LOD" stages for the pathfinding. Where you make one or more less detailed pathfinding-grid-overlayers, with a lower resolution. (for example: 1 field=4 lower grid fields, make it passable only when ALL of the lower grids fields are passable)
So for a distant search, the pathfinder would first look for the rough open area-connections, and then go one level deper in finding the exact way. (keeping inside the found path-fields of the "over"grid)