Sass function to calculate the color of a linear gradient at a specific point

_gradient-color-at.scss

///
/// Calculates the color of a linear gradient at a specific point.
///
/// @param {Color}  $start  - gradient’s start color
/// @param {Color}  $end    - gradient’s end color
/// @param {Number} $point  - point of the gradient (between 0 and 1, or 0% and 100%) at which we want the color
/// @return {Color}
///
/// @example scss
///   background-color: gradient-color-at(#BBE087, #DCDE85, 0.4);
///
@function gradient-color-at($start, $end, $point) {
  $error-message: "$point needs to be a percentage (0% to 100%) or a unitless number (0 to 1)";
  $unit: unit($point);
  // $point needs to be unitless or percentage
  @if $unit != "" and $unit != "%" {
    @error $error-message;
  }
  @else {
    // convert $point to fraction
    @if $unit == "%" { $point: $point / 100%; }
    // check if within bounds
    @if $point < 0 or $point > 1 { @error $error-message; }
  }

  $delta_h:         hue($end) - hue($start);
  $delta_s:  saturation($end) - saturation($start);
  $delta_l:   lightness($end) - lightness($start);
  $delta_a:       alpha($end) - alpha($start);

  @return adjust-color(
    $color:       $start, 
    $hue:         $point * $delta_h, 
    $saturation:  $point * $delta_s, 
    $lightness:   $point * $delta_l, 
    $alpha:       $point * $delta_a
  );
}