The white line dividing the boot topping from the grey hull paint was simply, and artistically painted in a box around the plimsol markings which are a legal requirement. As far as I am aware, painting a box around them like this was a unique feature to this ship, i don't have any photos of my own to show this clearly, but will look out some links in a day or when have more time if no one beats me to it, I know there is at least one photo showing it clearly in the original version of the warwick/flayhart book....