With curves you can adjust the brightness of individual colours for example here you can adjust the sky to give it a brighter more vibrant blue without affecting other parts of the image. Using Levels it will also change the gamma of the image affecting the midtones which Curves has not because I have put a point in at the mid tones (ie centre point)

Message edited on: 03/26/2005 05:41

And every one said, 'If we only live,
We too will go to sea in a Sieve,---
To the hills of the Chankly Bore!'
Far and few, far and few, Are the lands where the Jumblies live;
Their heads are green, and their hands are blue, And they went to sea in a Sieve.

Edward Lear
http://www.nonsenselit.org/Lear/ns/jumblies.html