A skin is an interchangeable colors for the theme. Each component part (eg. aside menu, brand, header, etc.) has changeable style need to be included. At a time, all 4 components are required. The skin demo can be previewed in online layout builder: https://keenthemes.com/metronic/preview/demo1/builder.html
At the moment, only demo1 support multiple skins which are dark and light. All other demos does not have separate skin colors.
The skins SCSS files can be found in this directory; [metronic]/theme/default/demo1/src/assets/sass/global/layout/**
