Bleu Nuit Nuage 50 is the name Audemars Piguet gives to a specific deep blue, and naming a colour rather than describing it is a signal that the house regards it as a distinct thing rather than a shade. On a guilloched dial that distinction has substance. The Grande Tapisserie grid works by catching light on hundreds of small raised squares and dropping it into the channels between them, so the perceived colour depends as much on the depth of the cut as on the pigment, and a very dark blue is the hardest case because the channels risk reading as black and the pattern disappears. This reference is rose gold at 37 mm with a diamond-set bezel and an integrated rose gold bracelet. Named dial colours are also comparatively rare in this collection. Most references describe their dials by shade, and reserving a proper name for one implies the house intends it to be recognised and asked for by that name, which is a different commercial intention from simply offering a blue watch. Collectors tend to adopt those names quickly, and the dial is now referred to by its own name more often than by its colour.
The case is rose gold at 37 mm, with the octagonal bezel set with diamonds and the eight visible screws left exposed through the setting. The bracelet is rose gold, integrated into the case, unset through every link and tapering to a folding clasp, so the stones are confined to the bezel and the rest of the watch is left as metal. The dial is Bleu Nuit Nuage 50 with the Grande Tapisserie pattern, and the interaction between a dark dial and a warm case is the substance of the reference. Rose gold applied hour markers sit on a field that is nearly black at low light and clearly blue in daylight, so the markers change in prominence as conditions change rather than holding a constant contrast. Royal Oak hands cross it. Against white gold the same dial would read colder and flatter, and the warm case is what keeps the blue from becoming grey. The bezel setting has to negotiate an octagon rather than a circle, presenting eight straight runs and eight corners where the spacing between stones is hardest to control. On a dark-dialled reference that setting also does more work than usual, since it supplies the only bright element on a watch whose display absorbs light rather than returning it.
The function set is hours, minutes, centre seconds and a date at three, which is standard across the 37 mm Selfwinding references. Winding is automatic. Retaining the date is a consequence of leaving the dial unset, since the fully jewelled references in this case size have to drop it, and a set bezel with an untouched dial is the configuration that keeps a watch usable while still being decorated. That is worth stating plainly because it is the practical difference between the three 15551 references and the two 15552 references rather than a difference of degree. The centre seconds hand also has a practical function on a dial this dark. Against a near-black field the hour and minute hands can be difficult to locate at a glance in poor light, and a continuously moving hand gives the eye something to find first, which is a small advantage but a real one. Dark dials are frequently criticised for legibility, and this is one of the ways a well-designed one answers the objection.
The current selection carries three 15551 references and this is the one that trades convention for colour. The other rose gold version uses a silver-toned dial, which is the classical choice and the one less likely to date, and the steel version uses grey. This reference is the only one of the three with a dark dial and it is the only place in the 37 mm group where a strong colour appears at all. Around them the 15550SR is two-tone with an unset bezel and the two 15552 references are snow-set across dial and bracelet. The group also shows how narrowly the collection is willing to vary a successful reference. Case, size, bezel treatment and specification are held identical across all three, and only the metal and the dial change, which means a buyer is choosing a colour rather than a watch and the comparison is unusually clean as a result.
The buyer for this reference wants a small gold Royal Oak that is noticed, which is a different intention from wanting one that is admired. Dark blue against rose gold is a high-contrast pairing and the watch reads clearly from across a room in a way the silver-dialled version does not. The diamond bezel reinforces that rather than softening it. This is the configuration that photographs best of the three, which is worth knowing in both directions, since a watch that images well often looks less remarkable in person and this one holds up better than most in that comparison. It is also likely to be the most divisive of the three within any given collection. A silver dial pleases almost everyone and offends no one, while a named dark blue is a stated position, and buyers tend either to want this specific dial or to have ruled it out before seeing it. There is very little middle ground, which makes it an easier reference to decide on than the silver-dialled alternative. Buyers who want it generally know before they see it, and buyers who do not are rarely persuaded by handling the watch. That clarity makes the reference straightforward to sell and straightforward to buy, which is not true of every configuration in the collection. It is also the version most often photographed, which has given it a visibility the other two lack.
