The Grand Seiko "UFA Diver Ushio 300" is packed with appeal! "Blue" or "Green," which will you choose?

The Grand Seiko Evolution 9 Collection Spring Drive UFA Diver Ushio 300, unveiled at Watches & Wonders Geneva 2026, is the smallest dive watch in Grand Seiko's history. For those looking for a small, lightweight dive watch that doesn't feel bulky, this model is sure to be a hit. The lineup consists of two models, with dial colors commonly known as "Ushio Blue" and "Ushio Green." Both are themed around the "sea," but they have distinct expressions. This time, we will delve deeper into the expressions and colors of the sea projected onto the dials of these two models, and introduce some recommended outfit combinations.

What are SLGB023 and SLGB025 "Ushio 300 Diver"?

　The Grand Seiko Evolution 9 Collection Spring Drive UFA Diver Ushio 300, which garnered attention at Watches & Wonders Geneva 2026, boasts the smallest diameter (40.8mm) in Grand Seiko's history of diver's watches. It is equipped with the new Cal.9RB1 movement of the Spring Drive UFA (Ultra Fine Accuracy) series, which was announced last year and boasts ultra-high precision with an annual deviation of ±20 seconds.

　There are three differences between this model and the previously released Cal.9RB2: the presence or absence of a calendar, the position of the power reserve indicator, and the shock-resistant shape of the rotor. The most noticeable difference is the omission of the calendar display, resulting in a cleaner design. Furthermore, by reducing the overall number of parts, it was possible to achieve a smaller diameter and thinner profile while still incorporating the necessary elements of a diver's watch (i.e., ensuring water resistance and a rotating bezel).

　And let's not forget the clasp specifications. The clasp features Grand Seiko's first "slide-lock extender with micro-adjustment mechanism" buckle. Am I the only one who thinks that's a long name? In short, this buckle has a 2mm x 3-step micro-adjustment mechanism and an 18mm diving slide-lock extender, allowing for an extension of up to 24mm.

　Furthermore, the buckle's logo also features a double-locking mechanism. On a personal note, I am a watch enthusiast. However, I haven't had much experience with dive watches. Therefore, I was honestly surprised by the clasp's mechanism.

　If you ask me what it was, I'm embarrassed to admit it, but... it took me about 20 minutes to find the extender function. When I finally found it, I was so impressed, I probably had a dopamine rush in my brain. I only realized there was an explanatory video on the official website after filming was finished. So, I'd like to share the information I managed to find on my own during those 20 minutes (see image below).

　The dial comes in two colors: "Ushio Blue" and "Ushio Green." The nickname "Ushio" is derived from the "ushio" (tide), the ocean current that nurtured Japan's abundant marine resources as an island nation, and both models feature a stamped pattern on the dial.

　The SLGB025 uses Epson's signature optical multi-layer coating for coloring, while the SLGB023 uses plating and lacquer. These colors represent the vast ocean surrounding the Japanese archipelago.

Explanation of the colors of the "Ushio 300 Diver"

　Both the SLGB023 and 025 use bright titanium for the case and bracelet. Bright titanium is often noted for its lightness and corrosion resistance, but its color is also distinctive. Compared to stainless steel, it has a lower brightness and a more subdued sheen, giving it a more refined appearance.

　The unique color of this bright titanium further accentuates the stamped pattern and subtle color variations on the dial. Regarding the stamped pattern, it uses the same tide pattern as the current models SLGA015 and SLGA023. Next, let's discuss the dial colors of each model.

Explanation of the dial color of the SLGB023

　The dial of the SLGB023, commonly known as "Ushio Blue," expresses how light gradually disappears as you dive deeper into the vast ocean, causing the color to change to a deeper shade. The gradient, which deepens from the center outwards, makes the stamped pattern in the center more visible.

　The color is a shade that many would immediately think of as the quintessential blue—a shade with reduced saturation (vividness), neither too flashy nor too dull. However, it's not just any blue.

　The appearance of the colors and patterns varies depending on the illuminance (a unit representing brightness, indicating the amount of light per unit area), allowing you to see different expressions from time to time, much like the sea (see image below).

　The SLGB023 is a model where the dial color changes significantly depending on whether it's in strong sunlight or shade. In sunlight, the vibrancy stands out, while in the shade, the embossed pattern becomes less prominent. It's as if it's projecting the image of a calm, deep ocean. The color of the ceramic part of the bezel also changes in the same way as the dial, but in sunlight, I could perceive a slight yellowish tint in the bezel's color.

　Now, regarding the ocean blue color represented by this dial, have you ever wondered why the ocean appears blue in the first place? I'll explain that later.

Explanation of the dial color of the SLGB025

　The dial of the SLGB025, also known as "Ushio Green," depicts the shimmering surface of water reflecting sunlight in shallow waters. Like the SLGB023, it features a design where the color deepens from the center outwards, but it also has an added gradient paint on the outer edge, making the central pattern more visible and giving it a wider range of colors than the SLGB023.

　The dial and bezel both appear to be a muted, yellowish-green, but in sunlight, the dial color becomes less yellowish and more vibrant. Therefore, the color change due to illumination is greater than that of the SLGB023 (see image below).

　The SLGB025 is another model where the dial color changes significantly between strong sunlight and shade. In particular, under strong sunlight, the gradation is more pronounced, and a subtle pearl-like shimmer appears in the center. This significant color change is not only due to the increased color intensity from the added gradation, but also to the multi-layer optical coating. What is this multi-layer optical coating? And why was green used to represent the surface of shallow water? These questions will be explained in the next chapter.

The same theme, yet so different!? Two models reflect the different expressions of the sea.

　To reiterate, both models are themed around the "sea." Of course, there are many kinds of "sea," but with a few exceptions, we generally perceive the sea as being "blue." However, when you scoop seawater in a bucket, it's not blue. Why is that?　

　First of all, as a premise, there is no such thing as "color" as an object in the world that humans can see. What exists is light, and the range of light that humans can perceive is called "visible light." Visible light is a rainbow gradient of "red, orange, yellow, green, blue, indigo, and blue-violet," and even light that appears white at first glance contains all of these colors.

　This light strikes an object, and only the reflected colored light is captured by the eye, which acts as a lens, and converted into nerve signals. Only when these signals are received by the brain can we perceive it as "blue"—that is, we can recognize the color.

　Now, let's get back to the main topic and delve deeper into the expressions of the sea projected by "Ushio Blue" and "Ushio Green," along with the mechanism by which these colors are perceived.

The blue of the sea as expressed by Ushio Blue. But why is the sea blue in the first place?

　As explained above, humans perceive color based on the light that enters their eyes. But what about underwater? Water molecules in the ocean have a tendency to absorb longer wavelengths of light (red, orange, and yellow). Therefore, when sunlight shines into the ocean, this light is absorbed.

　On the other hand, shorter wavelength "blue light" is not absorbed and penetrates deep into the ocean, scattering in all directions so that it reaches the human eye and we perceive it as "blue." As the water gets deeper, the blue light that remains until the end is gradually absorbed or scattered as the distance increases, and the amount of light decreases, making it appear as a "dark, deep blue."

The green of the water's surface as expressed by Ushio Green. The mysterious way the color changes as the water level changes.

　On the other hand, what about shallow waters? In shallow waters, light sometimes reaches the seabed before it is absorbed by water molecules. If the seabed is made of light-colored sand, the white sand will try to reflect all the light. In the process of this round trip, the water molecules absorb the longer wavelengths of light, from red to orange, leaving behind blue and green light, which appears as a greenish-blue to the human eye.

　Incidentally, the slightly cloudy, greenish seas often seen around Japan are said to be caused by phytoplankton. Because phytoplankton perform photosynthesis, they absorb red and blue light and reflect green light. It seems that the phytoplankton leave behind "green" light, while water molecules leave behind "blue" light, resulting in a greenish sea. The natural world is truly fascinating.

Learning from nature: What is optical multilayer coating?

　Optical multilayer coating, unlike conventional coloring methods using paint, is a technique that uses PVD (*1) to create multiple nearly transparent thin films on the surface of an object, thereby utilizing the properties of light to produce "color." It can artificially create structural colors that change depending on the angle, such as those seen in the feathers of birds and butterflies, or the scales of fish. Let's take birds as an example.

　The surface of a bird's feather has a nanometer-scale layer made of a protein called keratin. When light strikes this layer, some of the light is reflected by the surface, and the rest is reflected by the internal layers. This reflected light interferes with each other (*2), creating structural color, which appears depending on the viewing angle. Optical multilayer coatings allow you to freely change this viewing angle depending on the design.

*1 PVD: Abbreviation for Physical Vapor Deposition. A process of ionizing and depositing metal in a high-temperature vacuum.
*2 Interference: This is a phenomenon in which, when two or more beams of light that have traveled through multiple paths overlap, light of a specific wavelength reinforces itself while light of other wavelengths cancels each other out. This phenomenon also occurs on the surface of pearls and in soap bubbles.

　This technology creates a thin film that traces the uneven pattern of the dial, allowing for rich color expression while beautifully preserving the texture. The dial color is expressed using optical technology. Next, let's look at some styling ideas to enhance that dial color and enjoy fashionable looks.

A foolproof way to coordinate your watch!? Try "picking up colors"!

　The outfits I'm recommending this time use the classic watch styling technique of "picking up the dial color." For the SLGB023, I've picked up "blue," and for the SLGB025, I've picked up "green." However, instead of simply combining the same colors, I'll introduce two different outfits for each watch, varying the brightness and saturation of the colors.

Recommended outfits for SLGB023

　This outfit combines blue pants, with a slightly lower brightness and saturation than the dial color, with a not-too-bright red top, creating a contrasting color scheme. Although the hues are quite different, the reduced saturation of both colors creates a cohesive and calm overall impression. Conversely, if you want to create a more lively look, you can increase the saturation of the red.

　This outfit also combines a blue top in the same shade as above with light gray pants. Both the top and pants pick up colors from the watch (top → dial color, pants → band color). Matching the clothes, which cover a large area, with the watch creates a sense of unity in the whole outfit.

Recommended outfits for SLGB025

　This outfit combines khaki beige pants, which have a brighter dial color (especially the bezel color), with a gray top. Both the top and pants pick up colors from the watch (top → dial color, pants → band color). By increasing the brightness of the pants color, the watch stands out slightly, creating a sophisticated and mature impression.

　At first glance, this might appear as if the colors haven't been picked up at all. There is a slight shift in hue (color tone), but the mint green is a color with increased brightness and saturation of the dial color, and the white is a color with the brightness of the band's gray maximized.

　In other words, both the top and pants are coordinated to match the color of the watch. It's the same technique as the "gray x khaki beige" example above, but the impression might seem completely opposite. If you want a fresh and clean look, I recommend this one.

Wear the image of the sea on your arm. "Blue or green"—which will you choose?

　I hope I've conveyed the appeal of both the SLGB023 and SLGB025 models. This time I touched on the internal workings and exterior of the watches, but my former watch salesman spirit has been ignited, and there are so many other appealing features that I want to write more!

　When it comes to diver's watches, legibility and visibility are paramount, so one might not see the need for an elaborate dial. However, with this model, I felt Seiko's determination in that aspect. It's a model that could only have been created by Grand Seiko, a brand that embraces "THE NATURE OF TIME" as its brand philosophy.

　Summer is just around the corner. If you were to wear this watch, which of the two ocean scenes you've been looking for on your wrist, would you choose "blue or green"?

Author profile

Mutsuyo Ito
He provides a wide range of consulting services related to "products, places, and people" at sales sites, including color supervision and image consulting for watch manufacturers, personal color diagnosis at event venues, and customer service training. He holds numerous qualifications, including a Grade 2 watch repair technician, a J-color certified instructor, and a GIA AJP. He is the representative director of parakeITO Co., Ltd. Website:https://www.mutsuyo-ito-parakeito.com/