Bleu nuit nuage 50 is the only dial Audemars Piguet used in both metals of the diamond-set 37 mm Royal Oak. The steel references carry light blue, Bleu nuit nuage 50 and grey; the rose gold references carry silver-toned, Bleu nuit nuage 50 and khaki green. Every other dial in the line belongs to one metal or the other, and this one crosses. That is not an accident of scheduling. The colour was created for the fiftieth anniversary of the collection and named for it, and it functions as the signature of the entire programme rather than as one option among several, which is why it appears wherever the anniversary references appear. In steel with a diamond-set bezel it is the least expensive route to that dial in the 37 mm size, and it is also the version where the contrast between an industrial case metal and a set bezel is at its sharpest.
The case is 37 mm across and 9.1 mm thick in stainless steel, with the octagonal bezel set with diamonds. That height is identical to the plain 37 mm reference of the same generation, which is worth stating because the fully gem-set version of the same case reaches 10 mm. Setting the bezel alone costs nothing in thickness, since the stones occupy metal that was already there, where setting the dial and bracelet requires channels cut throughout and adds nearly a millimetre. The eight hexagonal screw positions survive the setting and remain the fixed points the run of stones works around. The dial is Bleu nuit nuage 50 with the Grande Tapisserie pattern, the larger of the two grids the collection uses, and on a deep blue ground the pattern reads as tonal depth rather than as pure shadow, with the recesses darkening and the brushed square tops holding the colour. White gold applied hour-markers and Royal Oak hands sit above it. The bracelet is integrated steel, tapering from the case with the alternating brushed and polished treatment that defines the collection, and closes on an AP folding clasp. Steel takes a harder, cooler polish than gold, so the diamonds read against a bright neutral rather than a warm one and the effect is closer to white on white than to stones on metal.
The function set is hours, minutes, centre seconds and a date. That is one function more than the fully gem-set references in the same size carry, since those omit the date rather than cut an aperture through a continuous stone surface. Here the dial is metal and the window causes no such problem, so the reference keeps the complication the collection has fitted since 1972. Centre seconds keeps the three hands on a single axis. The applied markers give the eye something to read against, which the gem-set references deliberately give up, and the combination of markers, a date and a legible dark dial makes this the most practical of the set 37 mm references to actually use. A diamond bezel does not interfere with any of that, because it sits outside the dial entirely.
The Royal Oak is the collection Audemars Piguet is built on, and the 37 mm anniversary references form a three-step ladder in how far the setting goes. The plain reference is unset at 9.1 mm. This reference sets the bezel and leaves the dial alone at the same 9.1 mm. The fully gem-set reference sets dial, bezel and bracelet in a single coloured stone and reaches 10 mm. Within the diamond-set tier the steel references run light blue, Bleu nuit nuage 50 and grey, and the rose gold references run silver-toned, Bleu nuit nuage 50 and khaki green, with each of the six anniversary references matched by a standard-catalogue counterpart that carries the same dial without the anniversary designation. A white gold version of the same case takes a different route again, with baguette-cut diamond hour-markers replacing the applied ones.
This reference suits a collector who wants the anniversary dial in the smaller case and does not want gold. Steel with a set bezel is a particular combination: the case metal argues for restraint and the bezel argues against it, and the watch sits in the tension between them rather than resolving it. That reads as deliberate rather than confused because the Royal Oak has always been a steel watch priced and finished like a gold one. Bleu nuit nuage 50 is the dial that ties the piece most directly to the anniversary programme, and choosing it in steel rather than rose gold puts the emphasis on the colour rather than on the metal. It appeals to someone who wants the set bezel without the full gem treatment, and who values keeping the date and the applied markers that the fully set references trade away. The anniversary designation ties production to the occasion rather than to an open catalogue run.
