Administration - Installation - Core: Property is in System Skinner but ignored

Hi, I'm playing around with ILIAS 6 (release 2020-05-18) and I added il-pagetitle-color, so that I can change the color of the site headline from the system skinner. Here's what I have done so far:

1. Read https://docu.ilias.de/ilias.php?ref_id=367&obj_id=75028&cmd=layout&cmdClass=illmpresentationgui&cmdNode=x&baseClass=ilLMPresentationGUI several times.


2. I created a custom skin through the GUI. As far as I can judge it, all required files and folders were created in ../ilias/Customizing/global/skin/myskin/


3. I added a property to ../myskin/myskin-variables.less (see below for a snippet)


4. The property appears in the system skinner GUI.


5. I change the property to e.g. "blue"


6. I run lessc and the property is ignored, ie. does not appear in the css file.

I guess I'm missing something between 5. and 6. Please note that the property in question -- il-pagetitle -- is served by some template from ILIAS. It's not mine. The preceeding line -- il-top-bar-color... -- is ILIAS default.

So, here's the concrete stuff I added to ../myskin/myskin-variables.less

//** controls text color of the "topbar" (the title of the ILIAS Installation)
@il-top-bar-color: white;
@il-pagetitle-color: white;

I expected something in ../myskin/myskin,css like this

.il-pagetitle {
color: white;
}

Further note, I also tried @il-pagetitle: white; 

BTW, is it just me or is there a lot of cruft in the System Skinner/less files that does not apply to version 6 anymore? Many many properties have no expression in the final HTML/CSS or are at least not discoverable with the usual web developer tools.

I assume I'm missing something very basic and I guess that I'm not familiar with LESS CSS is not helping either. So I'd appreciate any pointers.

Best regards
Cab