Built-in module sass:color

color.complement($color) - Returns the RGB
complement of $color.

@use 'sass:color';

// Hue 222deg becomes 42deg.
@debug color.complement(#6b717f); // #7f796b

darken($color, $amount) //=> color - Makes $color darker
lighten($color, $amount) //=> color - Makes $color lighter