I agree with those who are slightly disappointed with the darker areas on the Ocean Swirl, spoiling the overall marbled green/blue effects. However, this is a feature of all the pens I have made of the same type of material. I own several of the old Delta fusion pens with marbled exteriors (blue, green and brown in my collection, although there is also a fourth fuchsia coloured version). In each pen, there is a section of the barrel that is distinctly darker if not almost black, breaking up the overall pattern on the body of the pen. I think this is a natural effect of the resin barrel the manufacturers use and can't be avoided.
I have now got more used to this while using the pen (and admiring it as I make it slowly turn in my hand...) I see it more like a deep, dark patch of ocean, contrasting the mysterious depths of the seas with the lighter areas around the surface catching the sunlight... I also find the pen benefits from being used in slightly subdued lighting, like candlelight or a lamp of that strength.
I own the Renaissance Brown, the Vibrant Blue and the Ocean Swirl: each are wonderful creations and form something of a "family".
I wonder what Pelikan will create next? I would love to see a deep ruby red marbled 800 or even a really dramatic black version!