How do you change your log in grey screen?

I haven't tested this on Lion:

To replace login screen background:

1. Enter the following commands in Terminal, pressing Enter after each:
   • cd /System/Library/CoreServices
   • sudo mv DefaultDesktop.jpg DefaultDesktop_Old.jpg (enter password when prompted)
2. Quit Terminal
3. Rename desired image to DefaultDesktop.jpg
4. In Finder, drag and drop the image into /System/Library/CoreServices
5. When asked, click Authenticate and enter user name and password for your Admin-level account.
6. Restart

 

Unfortunately GGJ that doesn't work on Lion. Slightly different procedure:

To change the background of Mission Control, you'll want to replace /System/Library/CoreServices/Dock.app/Contents/Resources/defaultdesktop.png. You'll need to logout or execute killall Dock in the Terminal in order for this change to take effect.

To change the background of the login window and full-screen apps that have a linen background, you'll want to replace /System/Library/Frameworks/AppKit.framework/Versions/C/Resources/NSTexturedFullScreenBackgroundColor.png.

You may have to re-apply these changes again after installing OS X updates . Note that it changes more than just the login screen, so select the wallpaper accordingly.

 

It may be cheating, but you can also set it with Onyx.

 

I suspected things might have changed with Lion, so thank you for taking the time to dig out that info! I've bookmarked your post for future reference.

 

Ccrew is there a terminal execute for login window? i have tried your procedure with no luck