It would be cool if obj polypaint could be imported. I think Pixologic invented the way of putting it in objs with the MRGB lines and has become something like the standard format for meshes with vertex color information. A number of applications are already supporting it.
But… Zbrush (4R8) can only export polypaint . Import would be sooooo very useful as well 
btw I couldn’t find a good place to post feature wishes - if this is not welcome here, I’ll remove this post.
It’s not as convenient as your suggestion, but just a reminder that Zbrush can convert any applied texture into polypaint in the Tool >Texture menu. So if you were trying to get external color data into zbrush as polypaint and your model has UVs, you could do it like that.
Thanks Spyndel. Actual use case was I wanted to take an object that I sculpted and painted with sculptGL on my Android into ZBrush to continue working on it. So no UVs unfortunately.
You can use the PLY format plugin to import a PLY file with vertex color. Be aware though that the plugin is not compiled for 4R8 and Unicode so only ASCII (plain English) file paths will work.
Thanks will check this out!
Just wondering are there instructions out there how I could write/compile such a file format plugin myself?
4R8P2 seems to even lack OBJ vertex color export, as in there’s nothing in the ASCII format .obj file that looks like color comments. Must I turn it on somewhere? If it can’t import it back in though, I hardly need it since I’m trying to script sending meshes from Rhino Grasshopper to ZBrush so cannot use the PLY import plug-in script, or any other script besides the one I’m running myself.
Vertex color export in OBJ works for me in 4R8 P2. Obviously you need to have polypaint on the model and Colorize on. The data is basically a comment block at the end of the vertex list with #MRGB at the beginning of each line of hexadecimal values.