Hrolf Kraki's half-sister, Skuld, was born undersea to an elven woman descended from Ran. So Skuld is partly a personification of the sea? And, sure enough:
"...mostly one saw the eyes, large and long-lashed, a changeable green which could shift from almost blue to almost golden, like sea-waves." (Hrolf Kraki, pp. 125-126)
Not just blue eyes but eyes changeable in color like the waves of the sea. What could be more appropriate? Skuld's body expresses the medium from and within which she was born. But, probably at this point in the text, we hasten past the descriptive passage because we are keen to read the dialogue between King Hrolf and Skuld and to learn how he will tackle the tricky question of her alleged witchcraft - which also fits with her having an elven mother. Every word matters here, not just those inside inverted commas.
Addendum: In fact, see also here.