index.js
function(color, amount) {
    var hsl = this.toHSL(color);

    hsl.l += amount / 100;
    hsl.l = clamp(hsl.l);
    return hsla(hsl);
  }
function(color, amount) {
    var hsl = this.toHSL(color);

    hsl.l += amount / 100;
    hsl.l = clamp(hsl.l);
    return hsla(hsl);
  }
function ( color , amount ) { var hsl = this . toHSL ( color ) ; hsl . l += amount / 100 ; hsl . l = clamp ( hsl . l ) ; return hsla ( hsl ) ; }
Lighten or darken a color by a given amount

@param {Color} color
@param {Number} amount
@returns {Color} color
Lighten or darken a color by a given amount