This is because the 0.99 version of desktop-base writes a config line into /etc/default/grub to setup the fancy grub theme.
I've reverted this change in desktop-base 0.101 - but it didn't make it into the installer.
keeping the local version will get you the nice purpy grub theme installing the package maintainers version will get you the less nice boot menu. functionally it doesn't matter.
FWIW, once the new desktop-base is in the ugly grub theme will be there until I rebuild grub to add the proper code for including grub themes