WW1 Royal Navy: Below waterline colour?

[TCC]

Hi
Does anyone know anything about the medium violet-grey hull colouring below the waterline on (some?) RN WW1 capital ships? Put simplyhas anyone seen reference to this colour in other RN ships.. other than HMS LION? (it's noted on her N. Ough drawn plans). I've since seen a model of an IRON DUKE class that also had the hull belw the boot-topping painted mid violet-grey.

If they did indeed paint them mid grey, when did they phase in the 'red lead'?

Anyone? Thanks