Mixin to generate CSS to change the label colors in Trello. Meant to be used with Stylish or another runtime css modifier.

Trello-label-color-mixin.less

// Trello mixin to use with stylish or something.
// Changes the trello card label colors based upon color variables

// wrapped it all in one mixin just for fun - the outer mixin is only useful for cleanliness and organization

.make-card-labels(){

  // list of all label colors in Trello.  Variable name must remain as they are for this mixin to work properly.
  
@red:#CF4647;
@orange:#EB7B59;
@yellow:#CACF43;
@lime:#94CA3D;
@green:#44AA55;
@blue:#2B4E72;
@sky:#62BECB;
@purple:#9061C2;
@pink:#ED146F;
@black:#556270;

@text-color:#fafafa;
@text-shadow:0 -1px 1px rgba(0,0,0,.1), 0 1px 1px rgba(255,255,255,.1);

.card-label(@bg,@tc:~"#ffffff",@ts:~"0px 0px 0px transparent"){

  // selector to handle the background
  @selector:~"card-label-@{bg}";

  // selector for handling the box-shadow of selected labels
  @selected-selector:~"@{selector}.mod-selectable.selected";
  
  // selector for handling the text-color
  @text-selector:~"card-label.@{selector}";

  // converts selector text into value of color variable
  @bg-color:@@bg;
  // box-shadow color for when hovering over labels at label selection
  @bs-color:darken(@bg-color,40%);

  .@{text-selector}{
    // default text color and text-shadow - overwritable
    color:@tc;
    text-shadow:@ts;
  }
 .@{selector}{
    background:@bg-color;
    background-color:@bg-color;
  }

  .@{selected-selector}{
    box-shadow:-8px 0 @bs-color;
  }

}

// first-argument, variable text of desired color
// see not above - these variable names can't change
// second-argument - text-color
// third-argument - text-shadow for text
// second and third arguments are optional - defaults to white color and 0px transparent text-shadow

.card-label(black,@text-color,@text-shadow);
.card-label(blue,@text-color,@text-shadow);
.card-label(green,@text-color,@text-shadow);
.card-label(lime,@text-color,@text-shadow);
.card-label(orange,@text-color,@text-shadow);
.card-label(pink,@text-color,@text-shadow);
.card-label(purple,@text-color,@text-shadow);
.card-label(red,@text-color,@text-shadow);
.card-label(sky,@text-color,@text-shadow);
.card-label(yellow,@text-color,@text-shadow);

}

// execute main mixin function
.make-card-labels();