I'm sure you already know Sass is the new way to do Css. Use variables like you do in all your other programming languages and call your colors $medium-grey or $border-color. That way if you want to change them later, you can just do it in one spot. That and nesting and mixins and selector inheritance should be reason enough to have you convinced to make the switch.
And - setting up your Sass environment and making the move is not painful at all. Here is how you can get setup to use Sass with a sass-ready drupal theme.