Since the release of iOS 5, there have been a host of new Cydia tweaks, released to manually customize the iDevice according to each user's convenience. The latest tweak deals with the notification center and banners that appear on top of the screen.
The application (or the tweak) has been called Vexillum and allows the user to customize the background and font colors of the notification banner. Here are the steps to activate Vexillum on your device...
Step 1: First, go to Cydia -> ModyMyi repo and then download the Vexillum app; it is free
Step 2: Install the app on your iDevice
Step 3: Once you are done with the installation, go to Settings on your device
Step 4: Tap on the Vexillum application tab
Step 5: Choose from the host of customization options (the developer's e-mail has been provided, in case of problems)
Step 6: The desired changes/modifications take effect immediately; there is no need to reboot the iDevice
(Information from Jailbreakplus.com)