I think this depends a lot on what you want to do with the color.
If it is just for rendering I would be tempted to do it after the dop is simulated.
However, if for some reason you want to manipulate color data inside the dop network then try the setup below.
It's also worth mentioning that if you get vector fields into dops from sops then that data should be a volume. You can convert it into a volume either in sops or, as in my hip, with a gas microsolver.
It is probably best to add color during shading as well.
col.hipnc