Why does big black box appear over my GRUB2 theme when booting? - grub2

Question

I have created a GRUB2 theme, which gives me a screen like this:
But when I select one of the items to boot, before it boots, for about 5 seconds, it writes a big black box over the screen, like this:
Where is this black box coming from? It is clearly bigger than the menu box - is there some way I can stop it from appearing?
The files for the alien theme can be found on GitHub here:
https://github.com/edhartnett/alien_theme

Answer 1

Turns out that the big black box cannot easily be turned off.
It is the terminal-box, an area for text messages to appear. The theme and user have no control over it or its appearance.
There is reportedly a patch that can help, located here:
https://build.opensuse.org/package/view_file/openSUSE:12.3:Update/grub2/grub2-enable-theme-for-terminal-window.patch?expand=1
The patch was removed from GRUB2. You can review this bug report for reason why it was removed:
https://bugzilla.opensuse.org/show_bug.cgi?id=776244
I have not tried this patch or tried looking at the GRUB2 source code.

Answer 2

You can create a modified version of your background image and stick it in the terminal box for a seamless image, other than a tiny box outline:
For most users, the box will displays the messages:
Loading Linux %s ..." ${version}
Loading initial ramdisk...
For even more messages in the box (it's kind of neat), edit /etc/default/grub file find the line containing LINUX and remove quiet splash from the parameters. Save the file and run sudo update-grub.
Notes on recorded image
I attempted to use a cellphone with tripod but auto-exposure and auto-focus made it hopeless.
Then I installed VirtualBox 5.1 on Ubuntu 16.04 and used Video Capture. Unfortunately I had to scale grub down from 1920x1080 to 1024x768 for VB to work properly. As such the image is skewed in Virtualbox and you don't see the perfect fit that my normal grub boot has.
Edit your regular background image, cut most of the right side, repaste it shifted left and up. Save it as the modified background image.
In /etc/default/grub add the line GRUB_BACKGROUND= with the modified image location and name.
You might have to modify /etc/grub.d/00_header as per this thread. I did this on my machine.
The sample grub image is missing bootup messages because Virtualbox is intercepting and hiding them.
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