Sure. You’ll need to UV unwrap your model first. You’ll need to bring your exported model into another 3D modeling application to automatically unwrap it. Blender is free and can auto unwrap with “Smart UV Project”. ZBrush will give you a better result with “UV Master”, but it isn’t free.
To turn your vertex colors into a texture you can use a feature in MeshLab(which is free).
Once you’ve done those things you’ll have everything you need to create an MTL file. It’s a little complicated, but I hope that helps.
We hope to automate this process as much as possible in MasterpieceVR at some point.