Different Shades of transparent colors with Sass

input.scss

// Transparent Background
// From: http://stackoverflow.com/questions/6902944/sass-mixin-for-background-transparency-back-to-ie8

// Extend this class to save bytes
.transparent-background {
  background-color: transparent;
  zoom: 1;
}

// The mixin
@mixin transparent($color, $alpha) {
  $rgba: rgba($color, $alpha);
  $ie-hex-str: ie-hex-str($rgba);
  @extend .transparent-background;
  background-color: $rgba;
  filter:progid:DXImageTransform.Microsoft.gradient(startColorstr=#{$ie-hex-str},endColorstr=#{$ie-hex-str});
}

// Loop through opacities from 90 to 10 on an alpha scale
@mixin transparent-shades($name, $color) {
  @each $alpha in 90, 80, 70, 60, 50, 40, 30, 20, 10 {
    .#{$name}-#{$alpha} {
      @include transparent($color, $alpha / 100);
    }
  }
}

// Generate semi-transparent backgrounds for the colors we want
@include transparent-shades('dark', #000000);
@include transparent-shades('light', #ffffff);

output.css

.transparent-background, .dark-90, .dark-80, .dark-70, .dark-60, .dark-50, .dark-40, .dark-30, .dark-20, .dark-10, .light-90, .light-80, .light-70, .light-60, .light-50, .light-40, .light-30, .light-20, .light-10 {
  background-color: transparent;
  zoom: 1;
}

.dark-90 {
  background-color: rgba(0, 0, 0, 0.9);
  filter: progid:DXImageTransform.Microsoft.gradient(startColorstr=#E6000000,endColorstr=#E6000000);
}

.dark-80 {
  background-color: rgba(0, 0, 0, 0.8);
  filter: progid:DXImageTransform.Microsoft.gradient(startColorstr=#CC000000,endColorstr=#CC000000);
}

.dark-70 {
  background-color: rgba(0, 0, 0, 0.7);
  filter: progid:DXImageTransform.Microsoft.gradient(startColorstr=#B3000000,endColorstr=#B3000000);
}

.dark-60 {
  background-color: rgba(0, 0, 0, 0.6);
  filter: progid:DXImageTransform.Microsoft.gradient(startColorstr=#99000000,endColorstr=#99000000);
}

.dark-50 {
  background-color: rgba(0, 0, 0, 0.5);
  filter: progid:DXImageTransform.Microsoft.gradient(startColorstr=#80000000,endColorstr=#80000000);
}

.dark-40 {
  background-color: rgba(0, 0, 0, 0.4);
  filter: progid:DXImageTransform.Microsoft.gradient(startColorstr=#66000000,endColorstr=#66000000);
}

.dark-30 {
  background-color: rgba(0, 0, 0, 0.3);
  filter: progid:DXImageTransform.Microsoft.gradient(startColorstr=#4D000000,endColorstr=#4D000000);
}

.dark-20 {
  background-color: rgba(0, 0, 0, 0.2);
  filter: progid:DXImageTransform.Microsoft.gradient(startColorstr=#33000000,endColorstr=#33000000);
}

.dark-10 {
  background-color: rgba(0, 0, 0, 0.1);
  filter: progid:DXImageTransform.Microsoft.gradient(startColorstr=#1A000000,endColorstr=#1A000000);
}

.light-90 {
  background-color: rgba(255, 255, 255, 0.9);
  filter: progid:DXImageTransform.Microsoft.gradient(startColorstr=#E6FFFFFF,endColorstr=#E6FFFFFF);
}

.light-80 {
  background-color: rgba(255, 255, 255, 0.8);
  filter: progid:DXImageTransform.Microsoft.gradient(startColorstr=#CCFFFFFF,endColorstr=#CCFFFFFF);
}

.light-70 {
  background-color: rgba(255, 255, 255, 0.7);
  filter: progid:DXImageTransform.Microsoft.gradient(startColorstr=#B3FFFFFF,endColorstr=#B3FFFFFF);
}

.light-60 {
  background-color: rgba(255, 255, 255, 0.6);
  filter: progid:DXImageTransform.Microsoft.gradient(startColorstr=#99FFFFFF,endColorstr=#99FFFFFF);
}

.light-50 {
  background-color: rgba(255, 255, 255, 0.5);
  filter: progid:DXImageTransform.Microsoft.gradient(startColorstr=#80FFFFFF,endColorstr=#80FFFFFF);
}

.light-40 {
  background-color: rgba(255, 255, 255, 0.4);
  filter: progid:DXImageTransform.Microsoft.gradient(startColorstr=#66FFFFFF,endColorstr=#66FFFFFF);
}

.light-30 {
  background-color: rgba(255, 255, 255, 0.3);
  filter: progid:DXImageTransform.Microsoft.gradient(startColorstr=#4DFFFFFF,endColorstr=#4DFFFFFF);
}

.light-20 {
  background-color: rgba(255, 255, 255, 0.2);
  filter: progid:DXImageTransform.Microsoft.gradient(startColorstr=#33FFFFFF,endColorstr=#33FFFFFF);
}

.light-10 {
  background-color: rgba(255, 255, 255, 0.1);
  filter: progid:DXImageTransform.Microsoft.gradient(startColorstr=#1AFFFFFF,endColorstr=#1AFFFFFF);
}