Bleu nuit nuage 50 is the most widely issued dial in the 37 mm Royal Oak line, and this reference is its plainest form. The colour was created for the fiftieth anniversary of the collection and named for it, and Audemars Piguet used it more often than any other dial in the size: in plain steel here, in diamond-set steel, and in diamond-set rose gold, with each of those matched by a standard-catalogue continuation carrying the same colour without the anniversary designation. No other dial in the size appears across that many configurations, and none of the others crosses from steel into gold. What that means for this particular reference is that it is the entry point to the signature colour, the version with no setting anywhere and nothing between the dial and the case but the tapisserie itself.
The case is 37 mm across and 9.1 mm thick in stainless steel, with the plain octagonal bezel carrying the eight exposed hexagonal screws that have identified the model since 1972. They are secured from the caseback so the visible heads sit aligned rather than wherever the thread ends. Brushed faces meet polished chamfers on every edge of case and bezel, with each change of finish falling precisely on the line, and steel holds that boundary with a harder edge than gold does. The dial is Bleu nuit nuage 50 with the Grande Tapisserie pattern, the larger of the two grids the collection uses. On a deep blue ground the pattern reads as tonal depth rather than as pure shadow: the recesses darken toward black while the brushed square tops keep the colour, so the surface has range within a single hue rather than a flat field. That is the specific quality the colour was made for and the reason it carries the anniversary name. White gold applied hour-markers and Royal Oak hands sit above it. The bracelet is integrated steel, tapering from the case with the same brushed and polished alternation, and closes on an AP folding clasp. Steel is the metal the Royal Oak was designed in and the one the case geometry was worked out for, since the alternation of brushed and polished surfaces was originally a way of giving a steel watch the finishing standards of a gold one.
The function set is hours, minutes, centre seconds and a date, which is the configuration the Royal Oak has carried since the original and the one the fully gem-set references in this size give up. Centre seconds keeps the three hands on one axis and the date is worked into the dial rather than added at its edge. White gold markers against a dark blue field is among the stronger contrast pairings the size offers, better than silver-toned or light blue and comparable to grey, so this is one of the more legible references in the line. Nothing about the dial competes with the hands, because there is no setting anywhere on the watch to return light.
The Royal Oak is the collection Audemars Piguet is built on, and the 37 mm anniversary references form a ladder in how far the setting goes. This reference sits at the base, unset at 9.1 mm. The diamond-set version holds the same height, because bezel stones occupy metal that was already there. The fully gem-set version sets dial, bezel and bracelet in a single coloured stone and reaches 10 mm, dropping both the date and the applied markers to keep the stone surface unbroken. Across the plain steel references the dials are silver-toned, Bleu nuit nuage 50, grey and light blue; the diamond-set steel references run light blue, Bleu nuit nuage 50 and grey; the diamond-set rose gold references run silver-toned, Bleu nuit nuage 50 and khaki green.
This reference suits a collector who wants the anniversary colour without anything else attached to it. Steel, no setting, the smaller case and the dial the whole programme was organised around is about as direct a statement of the anniversary as the collection offers, and the absence of gold or stones makes the colour itself the only distinguishing element. That is a deliberate kind of restraint rather than an economy. It appeals to someone who wants a Royal Oak that reads as a Royal Oak first and as an anniversary piece second, and to someone who values a dark dial for legibility and for how little it changes across the day. Anyone wanting the same colour with a set bezel or in gold has those references available, which makes this a starting point rather than a compromise. It is also the reference against which the others in the colour are judged, since every configuration Audemars Piguet built on Bleu nuit nuage 50 in this size is this watch plus something added. The anniversary designation ties production to the occasion rather than to an open catalogue run.
