gistfile1.sass

$list-networks : facebook twitter;
$list-networks-colors : #3b5998k #00a0d1;

@function color-of($social-network) {
  $key: index($list-networks, $social-network);
  @return nth($list-networks-colors, $key);
}

.icon-block {
  @each $network in $list-networks {
    &.icon-#{$network} {
      background-color: color-of($network);
    }
  }
}