the grub splash screen is a graphical boot up instead of the text mode. having a grub splash screen is not only pretty but sort of gives continuity to the entire linux graphics experience. and this is how you do it
its a 2 step process:
the first step is to install the theme
yum -y install grub2-starfield-theme
the next step is to add a line as root to /etc/default/grub
echo "GRUB_THEME=\"/boot/grub2/themes/system/theme.txt\"" >> /etc/default/grub
then modify the line