Leaving Wall Colors Alone in Egress Model

How can I paint the colors of the walls in the egress model without them being lost when I do the prepare-fill?

Solution: 

The prepare-fill button creates 101 outliners with color set to gray. They walk across the screen with their pens down in order to reset the patch colors to gray in preparation for the flood-fill.
Orginal Spread Across TerrainOrginal Spread Across Terrain

The change is fairly simple. Instead of simply placing pen down and walking across the screen, the outliners need to watch the terrain they are walking over and have there pens down only when moving between walkable patches. If they are about to step onto a wall or off the wall they should have their pens up in order to leave the wall patch colors alone.
Leave WallsLeave Walls

Submitted by joshua on 9. January 2008 - 13:59