How to export vertex colors or vertex group as polygroup for export? I would like to know how is the correct process to export a 3D model with correct "vertex group" or "vertex color"  to use in zbrush as polygroups to make my work easy.

1 - first of all I modelled this bucket in blender to use as Insert multimesh. 



2 - the next step is create a "vertex paint" ?. 



3 - then I go for export menu ,  choose as obj file , but before , I apply 0,0,0 to (r,l,s transformations) and go to this tab (check if this board are correct , I do not know what's the effects in those blue box I ve marked).



4 -  Now , In zbrush there are not polygroup (one for the strap , one for the metal button and one for the main bucklet , I just see only one polygroup for all the object see the image).

5 - the most quick solution is to separate the mesh in zbrush and create differents polygroups manually for every bucket and his pieces, metal button and main strap. but I prefer to use blender with group previously.
Go to Edit Mode and select what you want to Polygroup.

Go to Object Data tab and click plus next to Vertex Group then assign with your selection active and name if you like.

On obj export make sure the Polygroup box is checked.



ZBrush doesn't use smoothing like Blender does you need to subdivide to make it look smooth.