Neutral colours are the foundation for the visual language that defines the overall tone of your application. It could be fully desaturated, slightly colder or warmer, or even tinted in a fancy way to support the brand.
Fills are the lightest shades in your arsenal and should be used as the main background colours.
Strokes are not supposed to fill large areas but outline or divide them.
Alt or alternative colours are semi-transparent ones and could be applied both as fills and strokes.
