This script uses the Knoppix background (which you can easily change on the CD, it's in knoppix/background.jpg) during boot *and* shutdown.

Also, shutdown is made faster by using poweroff -f (which should be fine as long as you are running purely from CD - otherwise you should take that part out before using the script.)

Call this script splash.sh, put it inside knoppix/ on your CD, choose a nice knoppix/background.jpg, and there you go. No more colorful Knoppix messages...

Code:
#!/bin/sh

#########################################################
#
# splash.sh 1.0
# by probono
# GPL
#
# burn this file to your Knoppix CD in /knoppix  
# and boot with cheatcode "splash"
# 
# displays knoppix/background.jpg
# during boot and shutdown
# and makes shutdown faster (by using poweroff -f)
# NO WARRANTIES, USE THIS ON YOUR OWN RISK
#
#########################################################

#
# display splash at boot time
#

fbi \
/cdrom/knoppix/background.jpg \
-t 1 --quiet --device /dev/fb0 < /dev/tty1 > /dev/tty1 2>/dev/null

#########################################################
# uncomment line below if you don't want
# xsession to be changed (e. g. if you have your own)
# exit 0
#########################################################

#
# modify xsession script to display splash at halt and be faster
#

mv /etc/init.d/xsession /etc/init.d/xsession.~
cp /KNOPPIX/etc/init.d/xsession /etc/init.d/xsession

perl -pi -e 's|# After xsession exits, end X-Server|sudo nohup fbi /cdrom/knoppix/background.jpg -t 1 --quiet --device /dev/fb0 < /dev/tty1 > /dev/tty1 2>/dev/null & \n poweroff -f|' /etc/init.d/xsession

#
# remove that voice
#

perl -pi -e 's|OGGPLAY=/usr/bin/ogg123|OGGPLAY=echo|' /etc/init.d/xsession
perl -pi -e 's|PLAY=/usr/bin/wavp|PLAY=echo|' /etc/init.d/xsession

#
# give control back to init
#

exit 0