I love the way the mangaka has been using the red color this story! It's so restrained, so purposeful. I love how willing this author is to experiment and push the limits of his work, even if not every experiment works out fully.
The standouts in this story are the repeated visual motif of the red and white cross (which yes, DOES form the flag of England—however unintentional that may be). It's the horror in the ocean, it's the horror on the boat (the religious fanaticism), it's just a really neat encapsulation of the "danger" in the story in this single geometric symbol.
That geometric motif is repeated on the page with all the birds—the way the red serves both as a highlight and a bit of a censor bar? Covering up the details with broad, geometric shapes,, gosh. I love this manga so much.