Hi,
Welcome to Shapeways!
In Scupltris, you can use the paint function, then export as .obj, import into MeshLab, then export as VRML97
or
Export the .obj from Sculptris, import into MeshLab, then use MeshLab's zpainting followed by exporting as VRML97
or
Export the .obj from Sculptris, import into
Wings3D for UV mapping - this is sketchy and can get frustrating when Wings3D crashes - I forget if Wings3D can export as VRML97, however MeshLab will import a UV mapped .obj for VRML97 export
It may also be worth looking at
Blender to see what that can do.
Paul