node_modules/bulma/sass/utilities/functions.sass

@function mergeColorMaps($bulma-colors, $custom-colors)
  // we return at least bulma hardcoded colors
  $merged-colors: $bulma-colors

  // we want a map as input
  @if type-of($custom-colors) == 'map'
    @each $name, $components in $custom-colors
      // color name should be a string and colors pair a list with at least one element
      @if type-of($name) == 'string' and (type-of($components) == 'list' or type-of($components) == 'color') and length($components) >= 1
        $color-base: null

        // the param can either be a single color
        // or a list of 2 colors
        @if type-of($components) == 'color'
          $color-base: $components
        @else if type-of($components) == 'list'
          $color-base: nth($components, 1)

        $color-invert: null
        // is an inverted color provided in the list
        @if length($components) > 1
          $color-invert: nth($components, 2)

        // we only want a color as base color
        @if type-of($color-base) == 'color'
          // if inverted color is not provided or is not a color we compute it
          @if type-of($color-invert) != 'color'
            $color-invert: findColorInvert($color-base)

          // we merge this colors elements as map with bulma colors (we can override them this way, no multiple definition for the same name)
          $merged-colors: map_merge($merged-colors, ($name: ($color-base, $color-invert)))

  @return $merged-colors

@function powerNumber($number, $exp)
  $value: 1
  @if $exp > 0
    @for $i from 1 through $exp
      $value: $value * $number
  @else if $exp < 0
    @for $i from 1 through -$exp
      $value: $value / $number
  @return $value

@function colorLuminance($color)
  $color-rgb: ('red': red($color),'green': green($color),'blue': blue($color))
  @each $name, $value in $color-rgb
    $adjusted: 0
    $value: $value / 255
    @if $value < 0.03928
      $value: $value / 12.92
    @else
      $value: ($value + .055) / 1.055
      $value: powerNumber($value, 2)
    $color-rgb: map-merge($color-rgb, ($name: $value))
  @return (map-get($color-rgb, 'red') * .2126) + (map-get($color-rgb, 'green') * .7152) + (map-get($color-rgb, 'blue') * .0722)

@function findColorInvert($color)
  @if (colorLuminance($color) > 0.55)
    @return rgba(#000, 0.7)
  @else
    @return #fff