Color scheme names can be translated (and have recently been) which is why the new KCM is built around color scheme file names.
However, other places, such as Look and feel package, especially third party ones, still rely on the color scheme name as key.
Also look for the untranslated name if a filename isn't found.

BUG: 403774

Changed to breeze dark look and feel which sets theme to "Breeze Dark", no longer get an error message because the file is actually "BreezeDark"

A LNF package can also ship its own fully custom color scheme that isn't system-wide installed, so perhaps this needs some additional changes later, such as "You are using 'whatever lnf package' which uses a custom color scheme.", instead of a warning/error message. (I knew that dumping all of that "Current" and "Default" logic would fall on my feet eventually :/)