Typo. Fixed in the Lua doc on the forum.
I did not notice since I only use the default skin myself, but looking at the code for the UI elements search algorithm, the order is "user skin override" (e.g. ~/.secondlife/skins/dark when using the "dark" skin), then "skin in use in installation folder" (e.g. "/usr/local/CoolVLViewer-1.26.22/skins/dark"), then "default skin in installation folder" (e.g. "/usr/local/CoolVLViewer-1.26.22/skins/default")... I added a "user default skin override" (e.g. "~/.secondlife/skins/default") step before the last "default skin in installation folder" one for the next releases...