[ferret_users] stipple in a less dense dot

To: Ansley Manke <ansley.b.manke@xxxxxxxx>, "ferret_users@xxxxxxxx" <ferret_users@xxxxxxxx>, "William S. Kessler" <william.s.kessler@xxxxxxxx>
Subject: [ferret_users] stipple in a less dense dot
From: Kelin Zhuang <kzhuang@xxxxxxxxxxxxxxxxx>
Date: Mon, 09 Apr 2012 16:31:31 -0700
Organization: The University of Arizona
Reply-to: kzhuang@xxxxxxxxxxxxxxxxx
Sender: owner-ferret_users@xxxxxxxx
User-agent: Mozilla/5.0 (X11; Linux i686; rv:11.0) Gecko/20120329 Thunderbird/11.0.1

Dear Ansley and all,

How can I stipple a region with less dense dots so that I can see thebackground color as well. I'm guessing I need change symbol.

plot/over/nolab/vs/symbol=dot/color=black
Best,
Kelin