See that box around the image below. It just doesn't work sometimes.
For this to work, you must be in Pages or Keynote. If you don't have Pages or Keynote on your Mac, you should. I love them so much more than Word or Powerpoint.
Click the X in the box and you are out of Instant Alpha.
If you notice, the image has a little bit left of white around the edges. I can click on the image again and go to Instant Alpha again to get rid of these areas.
Click on those little areas and you have an image without the white background.
Looks much better now!
Here's one more tip, if you accidentally change a color you don't want to change, just go up to the Edit menu and click on Remove Instant Alpha.
Hope this helps friends! Check out Katie's linky party for more techy tips.