Probably the easiest way to get all of the edges set back to the default material is use CleanUp 3 to remove edge materials.Then go back and paint only the edges you need to change. In future models, handle material application correctly and avoid the extra work you have created in this model.
What exactly do you mean by absence of a color by layer function. Color by layer is available in SketchUp and has been forever.
That allows you to establish specific colors for specific layers. Maybe you want to use red for layers assigned to components/groups that show demolition. Or a light gray for components/groups of things that are not involved in the project. Lots of ways to do that. Of course there’s no requirement to set the colors. You can just let SketchUp assign the colors randomly.