On Land

Environment Information
At Rill Architects we run ArchiCAD on Mac OS X. If you work at Rill, this is your stuff. If you don't, but you work in ArchiCAD, you may find something interesting. Anybody else, I don't know.
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Pen 50 is the poché pen. It is gray (80% +/- I think) in model and layout pen sets. It should be the background color of any cut fill in new construction. (Existing condition elements are white.)

That said, one of the advantages of pen sets is having black+grayscale output while the much more colorful model pens help you stay organized. So we have an alternate poché pen, #70, which is sort of tealy in model but looks exactly like pen 50 in layouts.

Elevator walls
The original intent for this pen was to distinguish multi-story walls (then new in Archicad 10) from their single-story brethren. I don't use multi-story walls as a rule, but I like them for elevators. In any case, the color difference reminds the use that when you edit this element there will be consequences on remote stories.

Lately I've been using them for other distinctive conditions.

Elevator walls
Modeling walls. For example, walls on the layer A Wall3 are usually needed to get a dormer to close in model. The color reminds you they don't inject their misleading selves into the output plans.

Profile Patch

Complicated 'patching' profiles. The color makes clear where the profiles meet the conventional elements.