That sounds like 'Highlight Source Markers' in the On-Screen Display Options.
It is an on screen visual only - it will not print.
There is another 'Marker Range' that just shows lines for the extents - again they won't print.
Barry.
One of the forum moderators.
Versions 6.5 to 25
Dell XPS- i7-6700 @ 3.4Ghz, 16GB ram, GeForce GTX 960 (2GB), Windows 10
Dell Precision 3510 - i7 6820HQ @ 2.70GHz, 16GB RAM, AMD FirePro W5130M, Windows 10