Grub 2 Splash Image

To add a background image to the Grub 2 boot menu and increase resolution...

From terminal:

sudo nano -w /etc/default/grub

To uncomment a line, remove the #. So uncomment the GRUB_GFXMODE line and you can change the graphics modes as follows if you like:

GRUB_GFXMODE=1280x720,1024x768,800x600

CTRL-X to exit, answer Y, then enter.

sudo nano -w /etc/grub.d/05_debian_theme

Change value after WALLPAPER to name of background image you want to use. Be sure to get the image and put in this directory. Mine shows:

WALLPAPER="/usr/share/images/desktop-base/BlueGlowTux_1280x720.png"

If you want to change the color of the menu text, change the first color in either of the color pairs:

COLOR_NORMAL="blue/black"
COLOR_HIGHLIGHT="yellow/black"

CTRL-X to exit, answer Y, then enter.

Now in terminal type

sudo update-grub

...and you're done.