How do I make the apple terminal window auto change colour scheme when I ssh to a specific server

Put following script in ~/bin/ssh (ensure ~/bin/ is checked before /usr/bin/ in your PATH):

#!/bin/sh

HOSTNAME=`echo $@ | sed s/.*@//`

set_bg () {
  osascript -e "tell application \"Terminal\" to set background color of window 1 to $1"
}

on_exit () {
  set_bg "{0, 0, 0, 50000}"
}
trap on_exit EXIT

case $HOSTNAME in
  production1|production2|production3) set_bg "{45000, 0, 0, 50000}" ;;
  *) set_bg "{0, 45000, 0, 50000}" ;;
esac

/usr/bin/ssh "$@"

Remember to make the script executable by running chmod +x ~/bin/ssh

The script above extracts host name from line "username@host" (it assumes you login to remote hosts with "ssh user@host").

Then depending on host name it either sets red background (for production servers) or green background (for all other). As a result all your ssh windows will be with colored background.

I assume here your default background is black, so script reverts the background color back to black when you logout from remote server (see "trap on_exit").

Please, note however this script does not track chain of ssh logins from one host to another. As a result the background will be green in case you login to testing server first, then login to production from it.

A lesser-known feature of Terminal is that you can set the name of a settings profile to a command name and it will select that profile when you create a new terminal via either Shell > New Command… or Shell > New Remote Connection….

For example, duplicate your default profile, name it “ssh” and set its background color to red. Then use New Command… to run ssh host.example.com.

It also matches on arguments, so you can have it choose different settings for different remote hosts, for example.

Here's a combined solution based on a couple of existing answers that handles the exit. Also includes a little extra if you don't want to deal with 16 bit color values.

This should be put in your ~/.bash_profile

# Convert 8 bit r,g,b,a (0-255) to 16 bit r,g,b,a (0-65535)
# to set terminal background.
# r, g, b, a values default to 255
set_bg () {
    r=${1:-255}
    g=${2:-255}
    b=${3:-255}
    a=${4:-255}

    r=$(($r * 256 + $r))
    g=$(($g * 256 + $g))
    b=$(($b * 256 + $b))
    a=$(($a * 256 + $a))

    osascript -e "tell application \"Terminal\" to set background color of window 1 to {$r, $g, $b, $a}"
}

# Set terminal background based on hex rgba values
# r,g,b,a default to FF
set_bg_from_hex() {
    r=${1:-FF}
    g=${2:-FF}
    b=${3:-FF}
    a=${4:-FF}

    set_bg $((16#$r)) $((16#$g)) $((16#$b)) $((16#$s))
}

# Wrapping ssh command with extra functionality
ssh() {
    # If prod server of interest, change bg color
    if ...some check for server list
    then
        set_bg_from_hex 6A 05 0C
    end

    # Call original ssh command
    if command ssh "$@"
    then
        # on exit change back to your default
        set_bg_from_hex 24 34 52
    fi
}

• set_bg - takes 4 (8 bit) color values
• set_bg_from_hex - takes 4 hex values. most of my color references I use are in hex, so this just makes it easier for me. It could be taken a step further to actually parse #RRGGBB instead of RR GG BB, but it works well for me.
• ssh - wrapping the default ssh command with whatever custom logic you want. The if statement is used to handle the exit to reset the background color.