I've tried to change resolution, colors and background image for my grub menu, but I get no background (well, just a black one, no image).... What am I doing wrong?

This is my grub.cfg (omitting the OS's part):

#
# DO NOT EDIT THIS FILE
#
# It is automatically generated by grub-mkconfig using templates
# from /etc/grub.d and settings from /etc/default/grub
#

### BEGIN /etc/grub.d/00_header ###
if [ -s $prefix/grubenv ]; then
  set have_grubenv=true
  load_env
fi
set default="${saved_entry}"
if [ "${prev_saved_entry}" ]; then
  set saved_entry="${prev_saved_entry}"
  save_env saved_entry
  set prev_saved_entry=
  save_env prev_saved_entry
  set boot_once=true
fi

function savedefault {
  if [ -z "${boot_once}" ]; then
    saved_entry="${chosen}"
    save_env saved_entry
  fi
}

function recordfail {
  set recordfail=1
  if [ -n "${have_grubenv}" ]; then if [ -z "${boot_once}" ]; then save_env recordfail; fi; fi
}

function load_video {
  insmod vbe
  insmod vga
}

insmod part_msdos
insmod ext2
set root='(hd1,msdos5)'
search --no-floppy --fs-uuid --set 42509bf9-f3e6-460a-8947-ec0f5c1fbcc8
if loadfont /usr/share/grub/unicode.pf2 ; then
  set gfxmode=1280x1024x24
  load_video
  insmod gfxterm
fi
terminal_output gfxterm
insmod part_msdos
insmod ext2
set root='(hd1,msdos5)'
search --no-floppy --fs-uuid --set 42509bf9-f3e6-460a-8947-ec0f5c1fbcc8
set locale_dir=($root)/boot/grub/locale
set lang=es
insmod gettext
if [ "${recordfail}" = 1 ]; then
  set timeout=-1
else
  set timeout=10
fi
### END /etc/grub.d/00_header ###

### BEGIN /etc/grub.d/05_debian_theme ###
insmod part_msdos
insmod ext2
set root='(hd1,msdos5)'
search --no-floppy --fs-uuid --set 42509bf9-f3e6-460a-8947-ec0f5c1fbcc8
insmod jpeg
if background_image /boot/grub/Serenity_Enchanted_by_sirpecangum.jpg ; then
  set color_normal=black/white
  set color_highlight=brown/light-gray
else
  set menu_color_normal=white/black
  set menu_color_highlight=black/light-gray
fi
### END /etc/grub.d/05_debian_theme ###

The selected image has been copied to /boot/grub/Serenity_Enchanted_by_sirpecangum.jpg with no luck. I'm for sure missing something (probably something obvious) but I don't really get it...