SASS has a lighten function along with other color manipulation utilities (e.g. darken) which are really easy to use.

pink-website.scss

$primary: #ff0000;

body {
  background-color: lighten($primary, 30%);
  color: darken($primary, 20%);
}

Which compiles into the following

body {
  background-color: #ff9999;
  color: #990000;
}

It takes two arguments; color and amount.

Reference