Background image manual grub.cfg
You need to add the next line to your grub.cfg
before the menus. Since it is custom made and you're not going to use update-grub
you shouldn't have any problem:
background_image /boot/Your_image.png
Now, if you want to have a different background for your distros, you just need to add the line in the menu. For instance, this is the part where my menus start; as you can see I have a default background before the menus so that when grub starts it has a background, and after that each menu/submenu has its own background:
background_image /boot/SolusOS-splash.png
set color_normal=white/black
set color_highlight=black/white
submenu "Debian 8.1 -->"{
submenu "Debian 8.1 i386 -->"{
background_image /boot/DebianLava-splash.png
set iso=/boot/ISOs/debian-live-8.1.0-i386-gnome-desktop.iso
....
EDIT: Here are my search path entries (mind the uuid is my usb's ID) don't know if this might be your issue:
set boot_uuid=D042-8A53
set root_uuid=D042-8A53
search --fs-uuid $root_uuid --set=root
search --fs-uuid $boot_uuid --set=grub_boot
if [ $boot_uuid == $root_uuid ]
then
set grub_boot=($grub_boot)/boot
else
set grub_boot=($grub_boot)
fi