: The N dial in fact has a weak to strong tinge of blue depending on the light.

Yep, by this point the N dial was actually catalogued as "deep blue", in the English brochures at least.

The earlier N watches are down as "charcoal" and have a different paint finish, with less obvious blue tinge, though even they can look a bit blue in some light. It was never N for noire in the second generation, ironically...

I think keeping the N designation was more down to tradition than anything - even the 1553, which is distinctly blue and considerably lighter than even a late 1153, is catalogued as 1553 N. We don't see the more accurate B suffix until the 3rd gen "barrels" come along and for second gen watches not until the same CdG dial is adopted for the 110.253 update of the 1153.

Interestingly, the 110.253 with silver dial is called G for grey, though to my mind the dial is plenty metallic enough to justify "S":