Apple iWork '08 - Manual (Page 53)

Chapter 1 Getting Started with Pages 53
As you drag, the selection grows to include the contiguous area that uses the same
color. You can control how much of the image is selected by dragging less or more.
4 Repeat step 3 until you achieve the desired effect.
You can restore parts removed from the image at any time.
To restore parts of an image:
m Choose Format > Remove Instant Alpha.
m Choose Edit > Undo Instant Alpha as many times as you want.
Dragging more here …
… selects more of
the image.