ConstIt covers every route layer: the route lines, waypoints, sections, guidance lines, summary bubbles and border crossings. Read it to find a layer's name and what it paints by default, not to spread into RoutingModuleConfig.layers, which says why.
The module builds its own layers per map, so on a dark style, under a theme or with a map typeface, the colours and fonts it draws differ from these.
The layers RoutingModule draws with its default configuration, on a light style that no theme or knob has recoloured.