I use a workaround: I assign a different background colour to each window. This can be done via the "Options" context menu each time you open a new window.
However, you can also automate. I've added the code below to my ".bashrc" to select the "next available" colour. The list of colours is simply a list of RGB values.
# Set the next available background colour
for COLOUR in 0,0,0 100,0,0 0,100,0 0,0,100
do
PIDFILE=/var/run/mintty-bgcolour-${COLOUR}.pid
PID=`[ -e $PIDFILE ] && cat $PIDFILE`
if ! kill -0 "$PID" 2>/dev/null
then
echo $$ > $PIDFILE
echo -ne '\e]11;'$COLOUR'\a'
trap 'rm -f '$PIDFILE EXIT
break
fi
done
unset COLOUR PIDFILE
Another workaround is to set the transparency in "options" on the window to, say, "Medium" and then check the box "Opaque when focussed". This sort of gives you a different background colour on all the windows except the active one.