Brother when I see it code, my <3 it breaks, you are repeating code!, please  refactor it. You can choose both create a mixing or  join the identifiers. 
```scss
@mixin paint_columns($color, $table, $ncolumn) {
  #{$table} th:nth-child(#{$ncolumn}) {
    color: black;
    background-color: $color;
    border-left-color: $color;
    border-right-color: $color;
  }
}
...
@include paint_columns(#A9A9A9, table, 3);
```

[look here for more information](http://thesassway.com/intermediate/leveraging-sass-mixins-for-cleaner-code)