I have been following tutorials on using NavMesh and they all show the mesh rendering a green surface that is navigable.
Im currently in UE 4.5.1 and my NavMesh is up and running, the AI characters will navigate correctly but the mesh does not render the green surface, so I dont really know what is included in the navigable area.
If the only issue is that the navmesh isn’t displaying in the editor, make sure that Navigation drawing is enabled in the viewport (Show->Navigation, or hotkey P). Also, keep in mind that even if there isn’t a navmesh, AI characters will still slide along geometry… so make sure that it’s actual pathfinding happening, rather than just “sliding around a box”.