config.inc.php
Almost all configurable data is placed in config.inc.php. If this file does not exist, please refer to the setup section to create one. This file only needs to contain the parameters you want to change from their corresponding default value in libraries/config.default.php.
If a directive is missing from your file, you can just add another line with the file. This file is for over-writing the defaults; if you wish to use the default value there's no need to add a line here.
The parameters which relate to design (like colors) are placed in themes/themename/layout.inc.php. You might also want to create config.footer.inc.php and config.header.inc.php files to add your site specific code to be included on start and end of each page.
Note
Some distributions (eg. Debian or Ubuntu) store config.inc.php in /etc/phpmyadmin instead of within phpMyAdmin sources.
Warning
Mac users should note that if you are on a version before Mac OS X, PHP does not seem to like Mac end of lines character (\r). So ensure you choose the option that allows to use the *nix end of line character (\n) in your text editor before saving a script you have modified.
Warning
These settings might have huge effect on performance or security.