If you would like to search by keyword in the U.S. Congressional Documents database, you can use the Advanced Search option at the top of the main page. From here use the Text option in the drop-dox box, enter the keyword into the first search box, and hit the search button.
You can also search with a keyword by using the Just search for drop-down that appears after typing in the main search bar at the top of the main page. For this type of searching, you would simply type colonization and hit the search button.