wrote a small typescript method that will do this - It will take an asset forge generated obj and mtl file, and generate a single obj file with vertex colors.
Obj file will potentially grow, as vertexes that are shared between different coloured faces will need to be duplicated.
I will publish the script if there is a request for it
Would it possible to export vertex colors when exporting an OBJ file ?
Threejs supports this format - where each vertex has a color value attached. It would enable users of threejs to efficiently mesh-merge many objects without having to deal with textures.
The format is described in https://github.com/mrdoob/three.js/issues/11422
( I am a dev - I can help out if needed )
