autonomic.zone/scss/utilities/color_utilities.scss

@function dynamic-color($color, $lightness: 50, $dark-color: $brand-black, $light-color: $brand-white) {
     @if (lightness($color) > $lightness){
        @return $dark-color; // Lighter background, return dark color
    }
    @else {
         @return $light-color; // Darker background, return light color
    }
}

@function tint($color, $percentage) {
  @return mix(#fff, $color, $percentage);
}

@function shade($color, $percentage) {
  @return mix(#000, $color, $percentage);
}

@mixin placeholder($color) {
	&:-moz-placeholder {
		color: $color; // Firefox 4-18
	}

	&::-moz-placeholder {
		color: $color; // Firefox 19+
	}

	&:-ms-input-placeholder {
		color: $color; // Internet Explorer 10+
	}

	&::-webkit-input-placeholder {
		color: $color; // Safari and Chrome
	}
}