If it's the same in the current version, you get to the System Colors section by:
Click on "Change skin colours" in the main section
"Edit Colours" window will pop up
"Show me the skin colour presets" will show in the top pull-down menu, click on the dropdown arrow to the right of that
"Show me the skin defined system colours" will appear in the dropdown menu, click on that
Color tiles will show in the window with the titles under them, e.g. "Menu Text", "Button Face", "Window Text"
Click on a color tile, then click on the "change color" button on the right side of the window
It may be slightly different now, I am after all a dinosaur, but hopefully that will get you there.