Modifying HSLA

darken($color, 5%)
lighten($color, 5%)

saturate($color, 5%)
desaturate($color, 5%)
grayscale($color)

adjust-hue($color, 15deg)
complement($color)    // like adjust-hue(\_, 180deg)
invert($color)

fade-in($color, .5)   // aka opacify()
fade-out($color, .5)  // aka transparentize()
rgba($color, .5)      // sets alpha to .5