Macbook notification banner smudge whenever the notification banner that appears on the top right of my screen appears, it's covered by a smudge. I can't find any other other answers online that deals with this problem and it's starting to really annoy me.
Try to completely disable Notification Center, reboot, then reenable.

To do so, (with caution, of course) try the following:


Launch the Terminal app from /Applications/Utilities, enter the following command, and press Return:


launchctl unload -w /System/Library/LaunchAgents/com.apple.notificationcenterui.plist


Reboot
Now re-enable Notification center:


launchctl load -w /System/Library/LaunchAgents/com.apple.notificationcenterui.plist


I have searched in vain to find any information regarding a .plist or other file containing appearance settings for notifications thinking that somehow these had become corrupt.