You can specify how colors should be treated when they overlap one another. You can set up how overlapping colors should be treated for the entire document, and then override the settings on a block by block basis.

1. Choose Preferences/Printing from the Document menu. Make sure Color Separations is checked.

2. Click on Knockouts. The Knockouts dialog box is displayed.
   To knockout objects so that underlying colors are removed from separations, choose Knockouts On from the Set Default popup menu.
   To overprint objects so that underlying colors remain in the separations, choose Knockouts Off from the Set Default popup menu.
   To knockout objects so that underlying colors are removed from the separations except where the overlying color is black, choose Overprint Black Only from the Set Default popup menu.

3. Click OK to return to the Printing Preferences dialog box, and click OK again.