Ubuntu shows 'Kubuntu' on boot

I recently updated my Ubuntu 12.10 setup to 13.04 using sudo do-release-upgrade.

After going through the process and rebooting, I was a little confused by the GRUB menu showing a "Kubuntu" option instead of "Ubuntu" as it usually did.

After choosing it, it then shows me a Kubuntu splash screen during the bootup (consisting just of a blue "Kubuntu"), but the subsequent login screen and desktop are fine.

I do have a KDE setup besides Unity (I had installed kubuntu-desktop way earlier when I was running 12.04), but I don't see why it should have affected the GRUB menu and the bootup splash screen!

Change Plymouth Splash Screen.

This is the initial splash screen you see at bootup. Different Plymouth themes can be found by searching for plymouth-theme in a Package Manager. Install a new one and manually select the theme you wish to use. The default Ubuntu theme is already installed.

sudo update-alternatives --config default.plymouth
sudo update-initramfs -u

Maybe you haven't removed kubuntu-desktop completely.

You can just remove the splash sudo apt-get remove kubuntu-artwork-usplash and start enjoying Raring Ringtail

Default value of variable GRUB_DISTRIBUTOR is set to
lsb_release -i -s 2> /dev/null || echo Debian by /etc/default/grub script while generating grub.cfg.

Check your /etc/default/grub.d/ directory for scripts which could overwrite this variable.

In my case it was /etc/default/grub.d/50_kubuntu.cfg which has been created by KDE Plasma Environment so I deleted it and generated grub.cfg again.

To solve this problem with GRUB, simply type into terminal:

sudo rm /etc/default/grub.d/50_kubuntu.cfg
sudo update-grub