In relation to documentation of projects, it may be useful to highlight a specific area of a Floorplan/Section/Elevation/3D Document with more than just lines/arcs.
Using semi-transparent fills in one solution to this requirement.

By default ArchiCAD has a number of rated fills patterns (25%, 50%, 75%) which mix the two pens assigned to the fill by various amount.

If the 'Fill Background Pen' is set to the special 'Transparent' pen (or pen '0') then the fill can applied as semi-transparent.
Some examples of these semi-transparent fills are shown below, both in Section and in a 3D Document.
(In both cases, the use of Display Order was used to ensure that the fill displayed in front of all the other geometry)

This is a reasonably simple process, but hopefully can be of benefit to you as you progress through your ArchiCAD projects..