.zshrc

...
alias ssh='~/bin/iterm2-set-background'
...

iterm2-set-background

#!/bin/bash
# ~/bin/iterm2-set-background
# Installation:
# 1. Save this script to /some/bin/ssh-background
# 2. chmod 755 /some/bin/ssh-background
# 3. alias ssh=/some/bin/ssh-background
# 4. Configure your host colors below.

set_color() {
  local HEX_FG=$1
  local HEX_BG=$2
  local OPACITY=$3

  local FG_R=`echo $HEX_FG | sed 's/../0x&,/g' | awk -F "," '{printf("%d",$1 * 257)}'`
  local FG_G=`echo $HEX_FG | sed 's/../0x&,/g' | awk -F "," '{printf("%d",$2 * 257)}'`
  local FG_B=`echo $HEX_FG | sed 's/../0x&,/g' | awk -F "," '{printf("%d",$3 * 257)}'`
  local BG_R=`echo $HEX_BG | sed 's/../0x&,/g' | awk -F "," '{printf("%d",$1 * 257)}'`
  local BG_G=`echo $HEX_BG | sed 's/../0x&,/g' | awk -F "," '{printf("%d",$2 * 257)}'`
  local BG_B=`echo $HEX_BG | sed 's/../0x&,/g' | awk -F "," '{printf("%d",$3 * 257)}'`

  /usr/bin/osascript <<EOF
tell application "iTerm"
   tell current session of current terminal
      set foreground color to {$FG_R, $FG_G, $FG_B}
      set background color to {$BG_R, $BG_G, $BG_B}
      set transparency to "$OPACITY"
   end tell
end tell
EOF
}

# ここでホストによる色を決める
# 最初のffffffが文字色
# 次の330000が背景色
if [[ "$@" =~ xxxx.com ]]; then
   set_color ffffff 330000 0.2
elif [[ "$@" =~ 192.128.88.88 ]]; then
   set_color ffffff 000033 0.2
fi

ssh $@

set_color ffffff 000000 0.2