Here's how you can get a fully transparent panel in Linux Mint 14.
1. Open a terminal window.
2. Type in the following commands, then hit Enter.
sudo cp -R /usr/share/themes/Mint-X ~/.themes/
sudo pluma ~/.themes/Mint-X/gtk-2.0/Apps/panel.rc
3. The second command will open the file in your default text editor.
4. Find both instances of this: Panel/panelbg.png
5. Comment out the both instances by placing a # at the beginning of each line.
6. Save the file.
7. Log out and then log back in. Your panel should now be fully transparent.
For more, see the original article at the link below.
Tips and Tricks for Linux Mint | Tech Support Alert