The terms dark, medium and light are subjective. What you call medium I might regard as dark.

I have numerous photographs of KGV in 1941. In some cases I have photographs of her taken the very same day but from different angles or heights or from different sides. In the sets of photographs taken the very same day you might say she was in dark grey in one photograph, but medium grey or even light grey in another. And in some individual photographs the tone of her grey can vary from dark to medium or even light depending where you look on her. It is hopeless.

So far as the Royal Navy was concerned the WW2 era Home Fleet grey, whether of the 507A or 507B formulation, was "GREY, DARK, Home Fleet shade"

For paints they regarded as medium greys you need to go to paints with RFs in the region 20% to 25%, So the official mix for Mountbatten Pink, or MS3, or the emergency mix of 50/50 507A & 507C