diff --git a/System/mdf.1m.sh b/System/mdf.1m.sh
index cbe05f97f..965e166fc 100755
--- a/System/mdf.1m.sh
+++ b/System/mdf.1m.sh
@@ -90,17 +90,17 @@ make_bmp_header() {
     # Common bits for version 1 and 5
     bmp_header+=(
         42 4d                   # "BM" magic
-        $_filebytes             # size of file
+        "$_filebytes"             # size of file
         00 00                   # reserved
         00 00                   # reserved
-        $_pixoffset             # offset of pixel data
-        $_headerbytes           # remaining bytes in header
-        $_width                 # width
-        $_height                # height
+        "$_pixoffset"             # offset of pixel data
+        "$_headerbytes"           # remaining bytes in header
+        "$_width"                 # width
+        "$_height"                # height
         01 00                   # 1 color plane
         20 00                   # 32 bits per pixel
-        $comp 00 00 00          # compression
-        $_pixbytes              # size of pixel data
+        "$comp" 00 00 00          # compression
+        "$_pixbytes"              # size of pixel data
         13 0b 00 00             # ~72 dpi horizontal
         13 0b 00 00             # ~72 dpi vertical
         00 00 00 00             # colors in palette
@@ -176,8 +176,8 @@ function rect() {
 }
 
 output_bmp() {
-    local _bmp=(${bmp_header[@]/#/'\x'})
-    _bmp+=(${pixels[@]/#/'\x'})
+    local _bmp=("${bmp_header[@]/#/'\x'}")
+    _bmp+=("${pixels[@]/#/'\x'}")
 
     local IFS=''
     #echo -ne "${_bmp[*]}" >/tmp/mtop.bmp
@@ -199,7 +199,7 @@ init_bmp() {
     if [ ${#pixels[@]} -ne $pixbytes ]; then
         pixels=()
         for ((i = 0; i < width * height; i++)); do
-            pixels+=(${curcol[@]});
+            pixels+=("${curcol[@]}");
         done
     fi
 }
@@ -212,6 +212,7 @@ osver=$(sw_vers -productVersion)
 
 # Colors in BGRA format
 fgcol=(00 00 00 ff)
+fgcol_alert=(00 00 00 88)  # semi-transparent.
 bgcol=(00 00 00 00)
 bmp_ver=5
 icontype=templateImage
@@ -222,14 +223,26 @@ if [[ $osver == 10.8.* ]]; then
     icontype=image
 fi
 
+# return the alert colour if alert condition is met.
+# else return foreground colour.
+# alert condition: free capacity < 2%. 
+determine_col() {
+  if (( $1 < 98 )); then
+  	retval=("${fgcol[@]}")
+  else
+  	retval=("${fgcol_alert[@]}")
+  fi
+}
+
 # Routines to draw simple progress-bar-like buckets for showing
 # capacity of disks, batteries etc.
 
 init_bar() {
     pixels=()
-    curcol=(${bgcol[@]})
+    curcol=("${bgcol[@]}")
     init_bmp $bmp_ver "$1" "$2"
-    curcol=(${fgcol[@]})
+    determine_col "$root_capacity"; col=("${retval[@]}")
+    curcol=("${col[@]}")
     rect 0 0 "$1" "$2"
 }
 
@@ -262,16 +275,16 @@ get_disk_stats() {
     local IFS=$'\n'
     local i dfdata dudata diskname
 
-    dfdata=($(df -H))
+    dfdata=("$(df -H)")
 
     IFS=$OLDIFS
-    for ((i = 0; i < ${#dfdata[@]}; i++)); do
-        line=(${dfdata[$i]})
+    for ((i = 0; i < "${#dfdata[@]}"; i++)); do
+        line=("${dfdata[$i]}")
         if [ "${line[8]}" = "/" ]; then
             root_capacity="${line[4]/\%}"            
         fi
         if [[ "${line[0]}" == /dev/* ]]; then
-            dudata=($(diskutil info "${line[0]}" | grep "Volume Name"))
+            dudata=("$(diskutil info "${line[0]}" | grep "Volume Name")")
             diskname="${dudata[*]:2}"
             disk+=("${diskname:-Untitled}")
             used+=("${line[2]}")