I don't use Celluclay for ground cover anymore, but
when I did use it, I remembered a "step" that Shep
Paine suggested in one of his soft cover "how to" books
that I have. Shep put earth colored paint, acrylics in
the Celluclay with the water when he was mixing it.
That way you already start with a ground color that is
the color of earth. Since celluclay can end up dry with
such a textured surface — if you wait to paint the
Celluclay after applying it, when it's dry — you will
find that in some places it is hard to get the brush
down into the deep holes or recesses of the Celluclay.
Thus putting paint in the Celluclay first is a good idea.