Background image when starting "the feather"

[clunga]

I understand it sound as a silly question, ;D ;D but I love to personalize my distros. In ubuntu or in Mint, I can set up a starting image when booting which is used as a background. Following the booting configuration /boot/grub/grub.cfg which states

nsmod png
background_image -m stretch /boot/grub_linux_lite.png
if [ "${recordfail}" = 1 ] ; then
  set timeout=30

and further on

[color=red]insmod png
if background_image /boot/grub_linux_lite.png;

I replaced the _linux_lite.png in the /boot folder, using the same dimensions and an extension .png, with an image of my choice.
Now, what I would like to do is to replace the "feather" image, that in Ubuntu approach, should be a background.png placed somewhere.
Thanks for your help