Thanks MoP, thats explained everything. So ideally you'd have to write a script for obj->obj? Haven't looked into it much but there could be a way to export vertex numbers and colour rgb values into notepad then use those in 3ds max, or any 3d app? or even automate the process?
It's not possible currently because they went with OBJ format, which doesn't support vertexcolour at all :) I guess if someone has some ZScripting skillz, it might be possible to write out the vertex colour data per vertex, and then re-apply it in another app, but that would rely heavily on vertex order staying correct in…