I agree that there were three tones and that the basic paint is the medium tone. From the time frame, one would expect 507A, B and C. But I have my doubts if this is the case here.
The Polish photo is rather dark. But the dark tone doesn't look too dark on this photo. It looks more like a medium gray, not like 507A.
The contrast between the pattern (dark tone) and the basic paint (medium tone) is not very high, as should be expected between 507A and C.
A ship painted mainly 507A and B would look pretty dark - in my opinion too dark for the Med.
So my impression is that the colors could probably be a basic paint of 507C and 507B for the pattern with Off-White at bow and stern. That would make a 2-tone scheme with fake bow and stern waves.
What do the experts think abaut this?