[Note: this answer works for CentOS. Fedora should be similar]
You add your own functions to the boot process either in /etc/rc.d/rc.local or as scripts in /etc/rc.d/init.d/ (see man chkconfig to see how the runlevel files are set up). Include /etc/rc.d/init.d/functions in your script and environment variables will be set with commands to set the following colours:
SETCOLOR_SUCCESS # green
SETCOLOR_FAILURE # red
SETCOLOR_WARNING # yellow
SETCOLOR_NORMAL # normal
So you added the following to rc.local:
echo "Hello world!"
You will get a red "Hello world!" in your boot sequence. For other colours, you would need to look up the ANSI escape sequences, which you can find on the Web easily enough.
"To err is human; to purr, feline."