It appears that Omega 5 includes a PHP based Sass compiler (phamlp) in the theme. When I upload a sass file into my sub-theme, it does not get compiled. How do I tell Drupal/Omega5/phamlp to compile Sass into CSS?
I can find no documentation on the Drupal site for this.
I figured it out. Edit the .info file to remove the line
stylesheets[all][] = style/css/base/site-branding.css
and add the line
stylesheets[all][] = style/scss/base/site-branding.scss
The system will now automatically process that .scss file. You can also add in any other .sass or .scss files in the same way.