cobalt blue (n) - a deep blue pigment containing cobalt and aluminum oxides
It is nothing more than a trinket to most, a family heirloom passed down through generations. A foreign necklace, Zuko sometimes hears people whisper, but she won't give it up.
They say it with slight disapproval, as though Katara should have to abandon all traces of her own history in order to rule by his side.
In older days, perhaps she would have had to do so, but now, today, as they rebuild, he won't let that happen. It pleases him to see his wife wearing her mother's necklace, because he doesn't love her for her compliance to his plans or to his culture; he loves her for her strong will and her pride in her heritage and her sharp mind that can see problems and solutions in ways that sometimes escape those raised and indoctrinated in Fire Nation glory.
(He loves her because she wears the set of hair combs he gave her on their engagement day pulled up in her new hairstyle along with the extra beads traditional among her people once a woman is married. He loves her because she taught him, early on in their marriage and at one of Iroh's many suggestions, how to fix her hair for her, and now they spend many early mornings talking and sitting on their bed as he combs and winds her long, dark hair into the style she has chosen to wear as Fire Lady.)
Everything in the Fire Nation is red and gold, the colors of fire and pride and power. On most days, Katara dresses as she pleases, and as she pleases is usually in blue. It's the color of the ocean, she shrugs, and I'm used to it.
She is always careful to wear Zuko's country's colors on special days, though, and when she plans to make important statements in council. A little flattery never hurts, she'll say with a smile as she kisses his cheek before they walk into the council room.
But even on those days where she is swathed in fire's colors, even on those very formal days where she deigns to give up her hair-beads out of respect for her new home, she will not give up her mother's necklace.
She insists it's not noticeable, just a small band of blue around her neck, but Zuko knows that it is, because everyone is watching her, always, to look for mistakes as she adapts to a new culture and a new way of life.
She handles the pressure remarkably well.
And even though some people advocate her complete acquiescence to Fire Nation culture, Zuko thinks it's important that she maintain some sense of difference, some sense of other, to remind his people that they are not the world dominators they once hoped to be.
This is a new world now, and a new era in Fire Nation history.
And having once handled the necklace so thoughtlessly, having once had the audacity to taunt Katara with her own heritage—having also learned that mentioning it tends to bring up embarrassing stories and insinuations he'd rather avoid, these days—Zuko swore long ago that he is never, ever saying anything that could be construed as negative about the necklace again.
It is precious to Katara, and therefore doubly precious to him.