The second method for surface labeling involves using colors in the input CAD files used to specify the LSC geometry. While STL files do not contain colors in their metadata, other file formats (e.g., DAE files) do. Figure shows an example of the color method, where the LSC edges are set as blue, while the incident surface is red. In this approach, only rays exiting from a blue edge would count as output rays. Although the surface normal method is convenient as it automatically detects edge surfaces, the colors method offers more flexibility in LSC design, as the user can manually define surfaces where PV cells could be installed.