Build a Drupal 7 site from planning through to giving people the privilege of posting pages and other content, with lots of key concepts covered and tips given along the way. Building this site is continued in Chapters 8 and 33.
The book instructs you to disable the Color and Overlay modules. At press time, disabling the Color module left the Slate color in tact. However, Drupal has changed and this is no longer the case. Now it reverts to the default blue color.
Correction or clarification:
In order to keep your site looking the way it should, you should leave the Color module enabled. Go ahead and disable the Overlay module as instructed.