Check out page 105/6 of the manual, this can be done.
The reference you gave uses the “Color” button on the toolbar. I’m talking about the Inspector down the left side. The coloured bar at the top used to have a drop-down list of the project’s colours.
This requires a modifier key to be held, have you checked if it changed by trying alt instead of ctrl/cmd ? I think the function is still there.
Cubase 9.5
Note the little arrow next to the instrument name at the top of the inspector. Click on that and a drop down list of all your colours appears.
Cubase 12
Cubase 13.
Arrow is missing.
These kinds of thing are minor but they involve muscle memory - when you’ve been doing something a particular way, whatever way that is, when it’s changed requires hours of adjustment. EG, when, in v10 the Preferences was moved from the File menu to the Edit menu it took me about 4 months to get used to it. (Yeah, I’m slow!) I still haven’t got used to the removal of the underscores in the menus - you can no longer use the keyboard to access the menu items in the standard Windows fashion.
But you can! New with C13.
hit alt when the mouse is not over a hot area (eg events area of editors) and the File menu lights up.
(reload page if nec. to see gif video)
I appreciate that you’re trying to help, but… Still no underscores to tell you which key to press next. It used to be 2 keys, now it’s multiple. That’s not an improvement.
Eons ago when letters were underlined there were items you could not reach.
Type the first letter of the items, all are accessible.