I agree with you about the uniforms, icarus. I like the way the Dawn Treader crew were costumed in the BBC dramas, actually. They all dressed a bit differently, a bit freely Narnian, and I would have liked to see that here, but I do like these uniforms... and how easily they lend themselves to fan-made costumes!
I do think that the blue-vested men are higher ranking. For one thing, there are many more red-vested men than blue vested, and for another, the two blue vests that I've seen are better quality... the red vests have simple metal buttons and leather trim, whereas the blue vests have fabric-covered buttons and are trimmed with a matching velvet color or with cord. Plus the blue vests have little sleeve caps that the red vests don't.
(given that Drinian, the highest ranking member of the crew, also wears red and that this photo here shows 3 different combinations of red/blue waistcoats/trousers - suggesting the rank/colour relationship might not be so exact as they made out)
I think you forgot to link the photo, but I think I know which one you're talking about. So far I've seen blue vest/red pants, red vest/blue pants, and blue vest/blue pants. I'm thinking they rank in that order, blue/blue being the highest, since the collar on the white shirt does seem to be an indication of rank, and the man in
this shot wears blue and blue and a collar. This makes sense, too, with the proportion of the crew wearing red/blue vs. blue/red or blue/blue... most are of "low" rank.
However, you do make a good point about Drinian! My original thought was that since his vest isn't at all like the vests of the crew (it's not the same fabric, it has a collar or lapels and it buttons up the front, double-breasted), I wondered if he wears a big blue coat over it.
And then I saw
this shot, and though it's a bit of a stretch, doesn't that look like him in a blue coat? Even though it's very dark and he's very much a silhouette, you can tell he's bald... and he's at the helm!
Another thing confirmed that thought...
Caspian wears a big duster-type coat, similar to what I imagined Drinian wearing.
ETA: Though on second thought, Caspian might just be wearing a long, loose sleeveless tunic-type coat, and the sleeves of the shirt underneath are a similar color. All the same...