Gordon Smith explains how to use a specific hatch pattern in AutoCAD to shade an area transparently.
"For quite a few years now, I’ve been shading with the Dots hatch pattern to achieve a transparent hatch pattern. We do a lot of work on top of aerial photos, and have found that using the Dots hatch allows us to still see the details of the photos, as well as any text that we may need to display. Getting the pattern scale right so that the opacity works out requires some trial and error. It usually works best to bring small text above the hatch for readability. Now that hatch transparency has been added to AutoCAD 2011 (and hopefully future versions as well), my tip may be useful only to those still working in older versions of the software."
Notes from Cadalyst Tip Patrol: Many times we need to shade an area to bring attention to it, but still allow linework, images, text, etc. to show through the shading. AutoCAD 2011 introduced a transparency setting for all objects (not just hatches). It works just like the linetype or color settings, and can be controlled by object or by layer.
There is a catch: When printing a drawing, the Print Manager must have the "Plot Transparency" option checked. Otherwise, no transparency settings will be applied to the print. (This has gotten me several times!) One way to avoid that setting mishap is to create a semi-solid hatch using the dot pattern. It creates a grid of dots whose density is controlled by the hatch pattern object's scale setting. Use the technique that suits your needs best.