The splash-fun theme sucks big times.
I say: yeah, it is a little thing, not worth to look into it at all, but something like that is really annoying.
Check here, and perhaps have your say:
http://raphaelhertzog.com/2010/11/12...-desktop-team/
You could try to set it here:
/usr/share/desktop-base/grub_background.sh
You could try this:
http://forums.debian.net/viewtopic.php?f=20&t=58239
update-alternatives --config desktop-grub.
In case both of that fails, i for one would try to rename:
/usr/share/images/desktop-base/desktop-grub.png
to moreblue-orbit-grub.png
A very dirty workaround, not sure if it works at all. But, like you say, the space-fun has to go away. No matter what it costs.
The whole space-fun joke was more funny if there was a nice and easy (= reliable ) way to change it in a sec.
The pity is that grub2 doesn't always do what one wants it to.
good luck.