One of the new features of MSFS compared to FSX and P3D is that you can specify vertex colors in your model as well. This means that just like a position or a normal, each vertex of the model can have its own color as well. This can be a more efficient way to set colors, as you don’t need different materials in that case.
Until now ModelConverterX did not support the concept of vertex colors. When you would load a glTF file which such colors they would be lost on export and ModelConverterX could also not render this information. That has changed with the latest development release. ModelConverterX can now import, export and render vertex colors as well. So this means you will no longer loose this information when working on your model in ModelConverterX.
Besides the glTF importer and exporter, also the Assimp importer and exporter have been updated to support vertex colors. So that means you can also read and write them to COLLADA and FBX files.