How to colorize the output of grep

Why does grep (and other tools) do this kind of thing by default yet (maybe via a build switch)?

#!/bin/sh

# colorsel
# make ANSI attribute/color string (the values only) - bjd
# not all attributes are used here

TPUT=tput

${TPUT} clear
#echo -en "33[H33[J"

# attributes:
# 0 = all attributes off
# 1 = intensity 2 (bold)
# 2 = intensity 0 (half-bright)
# 4 = underline on
# 5 = blink on
# 7 = reverse on
# 10 = G0/G1 charset
# 11 = 1st alternate font
# 12 = 2nd alternate font
# 21 = intensity 1 (normal, default)
# 22 = intensity 1 (normal, default)
# 24 = underline off
# 25 = blink off
# 27 = reverse off
# 38 = default fg, white underline
# 39 = default fg, underline off
# 49 = default bg

error()
{
echo -en "nError: $1"
ERROR=1
}

choose()
{
if [ ! "$4" = "-1" ]
then
PREV=$4
else
PREV=""
fi
${TPUT} cup $1 0
echo -en "Choose $3 number: $PREV" >&2
${TPUT} cup $1 $2
read answer
if [ "$answer" = "" ]
then
answer=$4
fi
if [ ! "$answer" = "-1" ]
then
${TPUT} cup $1 $2
echo $answer" "
fi
}

CHR="*"
echo -e "nttttBJ's colorsel %^)"
echo -e "nntttttBG"
echo -e " black red green yellow blue magenta cyan white"
echo -e " 40 41 42 43 44 45 46 47"
for FG in 30 31 32 33 34 35 36 37
do
if [ $FG -eq 33 ]
then
echo -n "F $FG"
elif [ $FG -eq 34 ]
then
echo -n "G $FG"
else
echo -en " $FG"
fi

for BG in 40 41 42 43 44 45 46 47
do
echo -en "[${BG};${FG}m${CHR}[m"

echo -en "[1;${BG};${FG}m${CHR}[m"
echo -en "[1;4;${BG};${FG}m${CHR}[m"
echo -en "[1;4;7;${BG};${FG}m${CHR}[m"
echo -en "[1;7;${BG};${FG}m${CHR}[m"

echo -en "[2;${BG};${FG}m${CHR}[m"
echo -en "[2;4;${BG};${FG}m${CHR}[m"
echo -en "[2;4;7;${BG};${FG}m${CHR}[m"
echo -en "[2;7;${BG};${FG}m${CHR}[m"

#echo -en "[4;${BG};${FG}m${CHR}[m"
#echo -en "[4;7;${BG};${FG}m${CHR}[m"
done
echo
done
ATTR_NRS="012345678"
echo -e " ${ATTR_NRS}${ATTR_NRS}${ATTR_NRS}${ATTR_NRS}${ATTR_NRS}
${ATTR_NRS}${ATTR_NRS}${ATTR_NRS}"
echo -e "tttt ATTR"


BG="-1"
FG="-1"
AT="-1"
while [ 1 = 1 ]
do
ERROR=0
${TPUT} cup 19 0
#${TPUT} ed
choose 18 26 "background" $BG
BG=$answer
choose 19 26 "foreground" $FG
FG=$answer
choose 20 26 "attribute " $AT
AT=$answer

if [ ! $BG = -1 ]
then
if [ $BG -lt 40 -o $BG -gt 47 ]
then
error "background out of range (should be empty or [40-47])"
fi
fi
if [ ! $FG = -1 ]
then
if [ $FG -lt 30 -o $FG -gt 37 ]
then
error "foreground out of range (should be empty or [30-37])"
fi
fi
if [ ! $AT = -1 ]
then
if [ $AT -gt 8 ]
then
error "attribute choice out of range (should be empty or [0-8])"
fi
fi

if [ $ERROR -eq 0 ]
then
${TPUT} ed
echo -n "Combined string : "
SEP=";"
if [ "$AT" = "-1" ]; then STR="";SEP="";
elif [ "$AT" = "0" ]; then STR="0";
elif [ "$AT" = "1" ]; then STR="1";
elif [ "$AT" = "2" ]; then STR="1;4";
elif [ "$AT" = "3" ]; then STR="1;4;7";
elif [ "$AT" = "4" ]; then STR="1;7";
elif [ "$AT" = "5" ]; then STR="2";
elif [ "$AT" = "6" ]; then STR="2;4";
elif [ "$AT" = "7" ]; then STR="2;4;7";
elif [ "$AT" = "8" ]; then STR="2;7";
#elif [ "$AT" = "9" ]; then #STR="4";
#elif [ "$AT" = "A" ]; then #STR="4;7";
fi

if [ ! "$BG" = "-1" ]
then
STR="${STR}${SEP}${BG}"
SEP=";"
fi

if [ ! "$FG" = "-1" ]
then
STR="${STR}${SEP}${FG}"
fi

echo ${STR}" "

if [ ! "${STR}" = "" ]
then
STR="33[${STR}m"
fi

echo -e "nnnIs ${STR}this33[m what you had in mind?"
echo -e "And then you could add a 5 attribute to make it 33[5m${STR}blink33[m..."

echo -n "Again? "
read answer
if [ "$answer" = "n" -o "$answer = "N" -o "$answer = "no" ]
then
exit
fi
fi
done