meaning of : in first line of the script

[w5000]

hello
below is beginning part of a sendfile script I am guessing is a shell script
what does mean : in first and again a few times more later (marekd in red)?

whole script

[COLOR=#EF2929]:[/color]
##########################################################################
# Title      :	sendfile - send file by e-mail
# Author     :	Heiner Steven <heiner.steven@odn.de>
# Date       :	1999-08-20
# Requires   :	getmimetype, metasend
# Category   :	Mail
# SCCS-Id.   :	@(#) sendfile	1.7 10/10/21
##########################################################################
# Description
#	Uses "metasend" to send files as MIME attachments
#
# Caveats
#    o	"sendfile" can handle file names containing whitespace characters,
#	but currently "metasend" cannot.
##########################################################################

PN=`basename "$0"`			# Program name
VER='1.7'

[COLOR=#EF2929]:[/color] ${SPLITSIZE:=104857600}		# 100 MB

usage () {
    echo >&2 "$PN - send file by e-mail, $VER
usage: $PN [-f] [-s subject] [-m mimetype] recipient file ...
    -f:  force sending of mail even for invalid recipients
    -s:  subject of the mail message
    -m:  mime-type (i.e. \"application/octet-stream\")

Multiple files may be specified. If no mimetype was given,
it is determined via a call to \"getmimetype\"."
    exit 1
}

 

[iggsterman]

it is a Null-statement.