Full lists of sass function can be found here

http://sass-lang.com/docs/yardoc/Sass/Script/Functions.html

[code]

$red = red;

@function border_color($in_val){

@return desaturate( darken( $in_val, 25%) , 50%);

}

.box{

padding: 30px

border: 1px solid border_color($red);

}

[/code]