diff --git a/bin/__build_sgr_code b/bin/__build_sgr_code
index 29deac6..60ed83f 100755
--- a/bin/__build_sgr_code
+++ b/bin/__build_sgr_code
@@ -1,4 +1,4 @@
-#!/usr/bin/env bash
+#!/bin/sh
 
 # This script will take an HTML compatible hex colour string and turn it into
 # a terminal sequence for true colour and other formats which best approximate
@@ -85,7 +85,7 @@ map vga-brightwhite "ffffff"
 enable_greyscale_cheat=0
 
 nocsi=0
-if [[ $1 == "no-csi" ]]
+if [ "$1" = "no-csi" ]
 then
     nocsi=1
     shift 1
@@ -103,17 +103,17 @@ dump_colors()
             *black*) text_color="ffffff" ;;
             *) text_color="000000" ;;
         esac
-        printf "%-24s${map[${key}]}  |" ${key}
+        printf "%-24s$(map ${key} )  |" ${key}
         printf "`$0 reset reverse bg:${text_color} fg:${key}`native-sample`$0 reset`|"
-        if [[ ! -v CSHENV_TERMINAL_COLORS ]] || (( ${CSHENV_TERMINAL_COLORS} >= 256 ))
+        if [ -z "${CSHENV_TERMINAL_COLORS+x}" ] || [ ${CSHENV_TERMINAL_COLORS} -ge 256 ]
         then
             printf "`env CSHENV_TERMINAL_COLORS=256 $0 reset reverse bg:${text_color} fg:${key}`8-bit sample`$0 reset`|"
         fi
-        if [[ ! -v CSHENV_TERMINAL_COLORS ]] || (( ${CSHENV_TERMINAL_COLORS} >= 16 ))
+        if [ -z "${CSHENV_TERMINAL_COLORS+x}" ] || [ ${CSHENV_TERMINAL_COLORS} -ge 16 ]
         then
             printf "`env CSHENV_TERMINAL_COLORS=16 $0 reset reverse bg:${text_color} fg:${key}`4-bit sample`$0 reset`|"
         fi
-        if [[ ! -v CSHENV_TERMINAL_COLORS ]] || (( ${CSHENV_TERMINAL_COLORS} >= 8 ))
+        if [ -z "${CSHENV_TERMINAL_COLORS+x}" ] || [ ${CSHENV_TERMINAL_COLORS} -ge 8 ]
         then
             printf "`env CSHENV_TERMINAL_COLORS=8 $0 reset reverse bg:${text_color} fg:${key}`3-bit sample`$0 reset`|"
         fi
@@ -127,15 +127,15 @@ cube_row()
 {
 	r_base=${1}
 	g=0
-	while (( g < 6 ))
+	while [ ${g} -lt 6 ]
 	do
 		u=0
-		while (( u < 3 ))
+		while [ ${u} -lt 3 ]
 		do
 			r=$(( r_base + u ))
 
 			b=0
-			while (( b < 6 ))
+			while [ ${b} -lt 6 ]
 			do
 				i=$(( 16 + ( r * 36 ) + ( g * 6 ) + ( b ) ))
 
@@ -163,7 +163,7 @@ greyscale_chart()
 	[ ${i} -ge 244 ] && txt=";30"
 
 	local k=$(( i + 12 ))
-	while (( i < k ))
+	while [ ${i} -lt ${k} ]
 	do
 		printf "[48;5;${i};37;1${txt}m%3i " ${i}
 		i=$(( i + 1 ))
@@ -176,7 +176,7 @@ color_chart()
 	i=0
 
 	# Base 16
-	while (( i < 16 ))
+	while [ ${i} -lt 16 ]
 	do
 		[ ${i} -gt 0 ] && txt=";30"
 
@@ -213,7 +213,7 @@ setup_color_depth()
         then
             use_3_bit=1
         else
-            echo "ERROR!" 1>&2 ; exit -1
+            echo "ERROR!" 1>&2 ; exit 255
         fi
     fi
 }
@@ -250,7 +250,7 @@ ansi_color()
 {
     if [ ${1} -gt 15 ]
     then
-        echo "ERROR!" 1>&2 ; exit -1
+        echo "ERROR!" 1>&2 ; exit 255
     elif [ ${1} -ge 8 ]
     then
         use_4_bit=1
@@ -269,17 +269,18 @@ ext_grey()
     grey_val=${1}
     if [ ${grey_val} -le 0 - ${grey_val} -gt 23 ]
     then
-        echo "ERROR!" 1>&2 ; exit -1
+        echo "ERROR!" 1>&2 ; exit 255
     fi
     ext_8_bit=$(( 232 + ${grey_val} ))
 }
 
-function ext_rgb()
+ext_rgb()
 {
     use_8_bit=1
-    red_ext_val=$((6#${1:0:1}))
-    green_ext_val=$((6#${1:1:1}))
-    blue_ext_val=$((6#${1:2:1}))
+    red_ext_val="${1%??*}"
+    tmp="${1#?}"
+    green_ext_val=${tmp%?*}
+    blue_ext_val=${tmp#?*}
     ext_8_bit=$(( 16 + 36 * ${red_ext_val} + 6 * ${green_ext_val} + ${blue_ext_val} ))
 }
 
@@ -288,7 +289,7 @@ ext_color()
     use_8_bit=1
     if [ ${1} -gt 255 ]
     then
-        echo "ERROR!" 1>&2 ; exit -1
+        echo "ERROR!" 1>&2 ; exit 255
     else
         ext_8_bit=${1}
     fi
@@ -298,17 +299,23 @@ rgb_color()
 {
     color=$1
     case $1 in
-        [0-9a-fA-F][0-9a-fA-F][0-9a-fA-F]) color=${1:0:1}${1:0:1}${1:1:1}${1:1:1}${1:2:1}${1:2:1} ;;
+        [0-9a-fA-F][0-9a-fA-F][0-9a-fA-F])
+			tmp="${color}"
+			color="${tmp%??*}${tmp%??*}"
+			tmp="${tmp#?}"
+			color="${color}${tmp%?*}${tmp%?*}${tmp#?}${tmp#?}"
+		;;
     esac
     # First split off the red, green, and blue components...
-    red_hex=${color:0:2}
-    green_hex=${color:2:2}
-    blue_hex=${color:4:2}
+    red_hex="0x${color%????}"
+    color="${color#??}"
+    green_hex="0x${color%??}"
+    blue_hex="0x${color#??}"
 
     # Convert to decimal...
-    red_dec=$((16#${red_hex}))
-    green_dec=$((16#${green_hex}))
-    blue_dec=$((16#${blue_hex}))
+    red_dec=$((${red_hex}))
+    green_dec=$((${green_hex}))
+    blue_dec=$((${blue_hex}))
 
 	if [ ${debug} -ne 0 ]
 	then
@@ -468,7 +475,7 @@ named_color()
 	debug_print "${name} -> ${mapped}"
     if [ -z "${mapped}" ]
     then
-        echo "ERROR!" 1>&2 ; exit -1
+        echo "ERROR!" 1>&2 ; exit 255
     fi
 
     rgb_color ${mapped}
@@ -506,8 +513,8 @@ build_sgr_code()
         fg:ext:rgb*) make_color 0 ext_rgb ${1#??????????} ;;
         fg:ext:*) make_color 0 ext_color ${1#???????} ;;
         # 12-bit color also supported
-        fg:[0-9a-fA-F][0-9a-fA-F][0-9a-fA-F]) make_color 0 rgb_color ${1:???} ;;
-        fg:[0-9a-fA-F][0-9a-fA-F][0-9a-fA-F][0-9a-fA-F][0-9a-fA-F][0-9a-fA-F]) make_color 0 rgb_color ${1:???} ;;
+        fg:[0-9a-fA-F][0-9a-fA-F][0-9a-fA-F]) make_color 0 rgb_color ${1#???} ;;
+        fg:[0-9a-fA-F][0-9a-fA-F][0-9a-fA-F][0-9a-fA-F][0-9a-fA-F][0-9a-fA-F]) make_color 0 rgb_color ${1#???} ;;
 
         bg:ansi:*) make_color 1 ansi_color ${1#????????} ;;
         bg:ext:grey*) make_color 1 ext_grey ${1#???????????} ;;
@@ -517,6 +524,8 @@ build_sgr_code()
         bg:[0-9a-fA-F][0-9a-fA-F][0-9a-fA-F]) make_color 1 rgb_color ${1#???} ;;
         bg:[0-9a-fA-F][0-9a-fA-F][0-9a-fA-F][0-9a-fA-F][0-9a-fA-F][0-9a-fA-F]) make_color 1 rgb_color ${1#???} ;;
 
+        ul:ext:grey*) make_color 2 ext_grey ${1#???????????} ;;
+        ul:ext:rgb*) make_color 2 ext_rgb ${1#??????????} ;;
         ul:ext:*) make_color 2 ext_color ${1#???????} ;;
         # 12-bit color also supported
         ul:[0-9a-fA-F][0-9a-fA-F][0-9a-fA-F]) make_color 2 rgb_color ${1#???} ;;