This is the way i have it set up.
My cavity Building Material uses and empty fill with a transparent background pen and a white foreground (hatch) pen.
This appears as an empty pen on plan.
With a Graphic Override that turns all fills to solid, the cavity will become white, so long as you do not override the foreground pen colour in the override.
When printing the white pen will not print.
If ever I do want solid filled cavities as well, then I just create a new override rule that changes the foreground pen colour as well.
The entire wall will become this override colour.
Barry.
One of the forum moderators.
Versions 6.5 to 27
i7-10700 @ 2.9Ghz, 32GB ram, GeForce RTX 2060 (6GB), Windows 10
Lenovo Thinkpad - i7-1270P 2.20 GHz, 32GB RAM, Nvidia T550, Windows 11