Inadvertently entered outline(?) mode--how do I exit it?

As Abhishek said simply using the keyboard shortcut Command/Control-Y will bring you back to the full color mode which is known as the Preview mode. Illustrator has always had two modes: Preview and Outline. You may find many instances in which working in Outline is actually preferable. It is especially useful when you want to make sure that two objects are perfectly aligned. Enlarging the Outline art makes it possible to see whether two lines are perfectly on top of one another. As one becomes more familiar with working in illustrator Outline mode can be a very handy tool to make use of. In addition to the key command you can toggle back and forth between Outline and Preview under the View menu.