To make them invisible in the editor, press V (or if you're not in the doodad palette, Ctrl + D)
To show the pathing of the map, press P (doesn't go together with V).
(Legenda: Blue = Unbuildable / Purple = Unwalkable/Unbuildable / Teal = Unflyable / Gray = Unwalkable/Unflyable/Unbuildable)