SASS Loop Background Colors, Change Text Color

My current project has me looping through an array of colors and applying them to boxes. So far that works - however, for the colors that are too dark, i need to change the text color to white. How can I make that happen?

$chartColors: $color__blue, $color__yellow, $color__grey,
  $color__orange, $color__gold, $color__light-blue, $color__turq,
  $color__pacific-grey, $color__green;
    
$chartColorsLength: length($chartColors);
    
.post-box,
.category-box {
  @for $i from 1 through $chartColorsLength {
    &:nth-of-type(#{$chartColorsLength}n + #{$i}) {
      background-color: nth($chartColors, $i);
      /* below doesn't work */
      @if background-color == $color__blue or background-color == $color__grey {
        p,
        a,
        h4 {
          color: #fff;
        }
      }
    }
  }
}