Generated by SassMeister.com.

SassMeister-input-HTML.jade

-for(var x=1; x<11; x++)
  div
    if x == 10
      h1 Fixed color
    else
      h1 :nth-child(#{x})

SassMeister-input.scss

// ----
// Sass (v3.4.12)
// Compass (v1.0.3)
// ----

// Just change this variable

$divbg: yellow;

// Function and other stuff


@function coloring($color, $type:"") {
  @if (lightness($color) > 50) {
    @if $type == "" {
      @return #000000; 
    }
    @else{
      @return darken($color, $type)
    }
  } @else {
    @if $type == "" {
      @return #000;
    }
    @else{
      @return darken($color, $type)
    }
  }
}

div{
  padding: 20px;
  font-size: 20px;
  margin: 10px 0;
  background:$divbg;
}
@for $i from 1 through 9 {
  $j: $i * 10;
  div:nth-child(#{$i}){
  color: coloring($divbg,$j);
}
}

div:nth-child(10){
  color: coloring($divbg);
}

SassMeister-output.css

div {
  padding: 20px;
  font-size: 20px;
  margin: 10px 0;
  background: yellow;
}

div:nth-child(1) {
  color: #cccc00;
}

div:nth-child(2) {
  color: #999900;
}

div:nth-child(3) {
  color: #666600;
}

div:nth-child(4) {
  color: #333300;
}

div:nth-child(5) {
  color: black;
}

div:nth-child(6) {
  color: black;
}

div:nth-child(7) {
  color: black;
}

div:nth-child(8) {
  color: black;
}

div:nth-child(9) {
  color: black;
}

div:nth-child(10) {
  color: #000;
}

SassMeister-rendered.html

<div>
  <h1>:nth-child(1)</h1>
</div>
<div>
  <h1>:nth-child(2)</h1>
</div>
<div>
  <h1>:nth-child(3)</h1>
</div>
<div>
  <h1>:nth-child(4)</h1>
</div>
<div>
  <h1>:nth-child(5)</h1>
</div>
<div>
  <h1>:nth-child(6)</h1>
</div>
<div>
  <h1>:nth-child(7)</h1>
</div>
<div>
  <h1>:nth-child(8)</h1>
</div>
<div>
  <h1>:nth-child(9)</h1>
</div>
<div>
  <h1>Fixed color</h1>
</div>