Bright blue is the only saturated color on this reference. Everything else Rolex builds here is a neutral, a pastel or a dark, and this is the one dial that commits to being a color outright, which on a case and bracelet made entirely from colorless metals is a considerable amount of weight for one surface to carry. Reference 278344RBR is the 31mm Datejust in a combination of stainless steel and white gold with a domed bezel set with diamonds, and this configuration pairs that blue dial with applied Roman numerals, on the Oyster bracelet. Bright blue is one of four grounds at this reference that are never offered set, so the color carries the dial on its own.
Saturated lacquer is harder to execute than it looks, because color that dense shows any variation in thickness as a change in tone, and the dial has to stay uniform across its whole diameter for the effect to work at all. Rolex applies it opaque, so there is no depth to the surface and no sense of looking into the dial the way a gradient or a stone invites, which produces a field of pure color with the numerals sitting on top of it rather than within it. The Roman numerals are applied white gold and faceted, drawn for this case size rather than scaled from another, and against a saturated ground they read as bright metal shapes with clear separation, the most straightforward marker-to-ground relationship on the reference. The case is a combination of stainless steel and white gold, the least visible two-metal pairing Rolex makes, and the bezel is white gold set with diamonds, so the stones cover most of the only surface where the second metal would be identifiable. That leaves the dial as the only element on the entire watch with a color at all. The bracelet is the Oyster, three broad flat links brushed across the top with polished flanks, and the date sits at three under the Cyclops lens on a matched disc. White gold is also considerably denser than steel, so the bezel here is noticeably heavier than a steel one of the same dimensions, and that weight is the one way the second metal announces itself on a watch where it cannot be seen. Rolex casts its own gold in a foundry on its premises, which is why it can hold an alloy to a consistent color across decades of production rather than across a single batch. The bezel stones are seated individually into recesses cut in the gold rather than dropped into a preformed channel, which on a ring this size means tighter tolerances than a larger bezel would demand.
The Datejust shows the date and nothing else. A single aperture is what allows a full Roman sequence to fit, and the date at three displaces the numeral that would otherwise sit there. The Cyclops lens above it has been part of the model since 1953 and remains the most recognizable thing about it at a distance. The date changes instantaneously at midnight rather than creeping through the surrounding hour, the feature the Datejust introduced in 1945 and the one it takes its name from. Correction runs through the winding crown without moving the hands, hand winding uses the same crown with no separate position to learn, and nothing the watch asks for requires a tool. The movement is self-winding with a power reserve of approximately 55 hours, an engineering result on a movement built to fit a 31mm case rather than a figure carried down the range, since a smaller barrel has less room to store energy. The crown screws down against the case, and the Oyster closes with a concealed clasp folded away inside the links. A movement of this size gathers less from the same wrist movement than a larger one, so the watch prefers regular wear to rotation. Correction takes seconds and requires no tool.
The Datejust arrived in 1945 as the first self-winding wristwatch to show the date in a window, and the 31mm case sits between the 28mm Lady-Datejust and the 36mm original. The 278000 generation replaced the 178000 series in 2018 with a revised case and bracelet. Strong dial colors are a comparatively recent development within the model, which ran on silver, white, champagne and black for most of its history with stone dials as the occasional exception. Blue has become the color Rolex reaches for first when introducing a new dial treatment, which gives this configuration a place in a wider pattern rather than standing on its own. Within the generation, 278344RBR is the steel and white gold reference with a diamond-set domed bezel. The 31mm case is also the least discussed of the three Datejust sizes and the one that has quietly absorbed most of the demand that used to go to the smaller references. Roman numerals have never been the volume choice across the model's history, which is part of why they still read as considered. Bright blue is one of seven grounds this reference offers unset, and one of four never built with stones on the dial in any configuration.
The buyer for this wants the watch identifiable at distance. Blue at this saturation carries across a room and the Roman numerals register as bright bars against it, so the whole watch resolves quickly and from further away than any gem-set dial here manages. That is a different proposition from the nacre and set dials on the same reference, which reward close inspection and lose most of their effect beyond arm's length. It is also the least fussy of the colored dials to live with, since a solid lacquer surface shows no variation between examples and none over time, and on the Oyster it stays a watch rather than becoming an occasion. Buyers who find the neutral dials on this reference too reticent and the gem-set ones too decorative generally end up here, since it is the only configuration that is emphatic without being ornamented. It takes two of the thirty-two rows here.
