I installed Ubuntu Mate on my Ubuntu 15.04 install just to try it out. It's pretty nifty, but it's replaced my minimal grub theme (with a purple background) with a gray-green menu I don't like in the least. I tried using Grub Customizer to change the look of Grub but I'm not having much success: the only theme that's available in Grub Customizer is the Ubuntu Mate one, and my efforts at a custom theme aren't working very well (for some reason my 1920x1080 wallpapers are not being properly rendered). Any thoughts on how I can get the minimalistic grub menu that comes with ubuntu unity back?
The default theme is provided by
plymouth-theme-ubuntu-logo. Install it:
sudo apt-get install plymouth-theme-ubuntu-logo
To set it as the default, run:
sudo update-alternatives --config default.plymouth
/lib/plymouth/themes/ubuntu-logo/ubuntu-logo.plymouth in the menu.