I took my Grub Fingerprint theme and created a background image that is really compatible with Grub 2. It comes with an install script, so you just need to unpack it and run
$ sudo ./install.sh
to get it working. To uninstall the background there is an uninstall script as well.
It worked perfect for me but if there are any problems please give me your feedback.
Here is the package: grub2-fingerprint-0.1
Next thing to do is to port the Usplash theme to Plymouth.