Set a variable in Sass depending on the selector

If you really want to get hacky you could also define your different color schemes in a single variable like $scheme1: class1 #333 #444, where the first value is always the name, and that is followed by all the colors in that scheme.

You can then use @each:

// Define your schemes with a name and colors
$scheme1: class1 #444 #555;
$scheme2: class2 #666 #777;
$scheme3: class4 #888 #999;

// Here are your color schemes
$schemes: $scheme1 $scheme2 $scheme3;

@each $scheme in $schemes {
  // Here are the rules specific to the colors in the theme
  body.#{nth($scheme, 1)} .content {
    background-color: nth($scheme, 2);
    color: nth($scheme, 3);
  }
}

This will compile to:

body.class1 .content {
  background-color: #444444;
  color: #555555; }

body.class2 .content {
  background-color: #666666;
  color: #777777; }

body.class4 .content {
  background-color: #888888;
  color: #999999; }

Obviously if you don't want to combine body.class1 and .content in your selectors, you could just specify a mixin content($main, $default) and call it inside the @each using nth just like in the above code, but the point is you don't have to write out a rule for each of your classes.

EDIT There are lots of interesting answers on Creating or referencing variables dynamically in Sass and Merge string and variable to a variable with SASS.

as sass documentation explain nicely (https://sass-lang.com/documentation/variables):

• Sass variables are all compiled away by Sass. CSS variables are included in the CSS output.

• CSS variables can have different values for different elements, but Sass variables only have one value at a time.

• Sass variables are imperative, which means if you use a variable and then change its value, the earlier use will stay the same. CSS variables are declarative, which means if you change the value, it’ll affect both earlier uses and later uses.

We may take advantage of that using a combination of sass and css variables to achieve what you want:

//theme colors
$red-cosmo: #e01019;
$green-cosmo: #00c398;
$primary-color: var(--primary-color);
body{
  --primary-color: #{$red-cosmo};
}
body.univers-ride{
  --primary-color: #{$green-cosmo};
}

So when I call my sass variable $primary-color, it will print as my css variable "var(--primary-color)" that will expand as $green-cosmo only if my body has the "univers-ride" class else it will be $red-cosmo the default color.

You can also create a mixing that use the ampersand parent selector. http://codepen.io/juhov/pen/gbmbWJ

@mixin color {
  body.blue & {
    background: blue;
  }
  body.yellow & {
    background: yellow;
  }
}

I think a mixin is the answer. (As I wrote, variables won’t work.)

@mixin content($color-default, $color-main) {
  background: $color-default;
  color: $color-main;
}

body.class-1 {
  @include content(#444, #555);
}

body.class-2 {
  @include content(#666, #777);
}

That SCSS compiles to this CSS:

body.class-1 {
  background: #444444;
  color: #555555; }

body.class-2 {
  background: #666666;
  color: #777777; }

If you wanted to group the color values together in your SCSS file, you could use variables in conjunction with the mixin:

$color-1: #444;
$color-2: #555;
$color-3: #666;
$color-4: #777;

body.class-1 {
  @include content($color-1, $color-2);
}

body.class-2 {
  @include content($color-3, $color-4);
}