Reading of these wonderful performances of Jewels I was lead back to Laura Jacobs's "Balanchine's Castle" in The New Criterion, written eight years ago. Since that publication is usually a for-pay-only read these days, I was surprised to find that the article is still freely available in its entirety.
Jacobs in this article elaborates on Croce's theory that relates Jewels to Cluny's Unicorn Tapestries. Quoting Suzanne Farrell's autobiography Jacobs says
Balanchine took her to the Musée de Cluny to see The Lady and the Unicorn tapestries. Of the sixth tapestry she writes: “He loved the title A Mon Seul Désir [“To My Only Desire”] and said he wanted to make a ballet for me about the story of the unicorn.” It seems safe to say that “Diamonds” is that ballet, or rather, that Jewels is, that it was the white glow of the unicorn that Balanchine chased into the forest, only to find himself in a thicket of haunting and hunted creatures.
At NYCB's 1998 recension, Emeralds, especially, had lost its way. Jacobs tries to bring it back by explaining
“Emeralds” finds Balanchine deep in the poetic realm of Coleridge and Keats—it’s an enchanted forest filled with Darke Ladies and muses on the make—and in the compositional genre of hunt and vision scenes (Swan Lake, The Sleeping Beauty) and twilight gardens (Serenade). It is a work of trance and transparency. You feel you can reach through the green of “Emeralds” and grasp nothing.
Karinska's costumes for the ballet are both loved and not-so-loved by viewers. Jacobs explains their association with the ballet's "story", beginning with, but going beyond
The lighting design of Ronald Bates and the costumes of Madame Karinska work in brilliant complicity; Bates makes palpable poetic weather of his lighting, which Karinska’s costumes either sink into (“Emeralds”) or bounce out of (“Rubies”) or refract (“Diamonds”). And so the French-opaline greens that soften and blur the edges of “Emeralds” create a plush and pillowy space, a netherworld love-nest. The sharp red of “Rubies” practically vibrates against a cindery light; it’s a red with black in it, royal and radical at once. And the snow-crystal radiance of “Diamonds” is underlit with a blue as pale as a vein in a slim white wrist.
This is a long, complex article; I've given these quotes to whet the appetite. If for no other reason, it is worth a read for the shocking--and moving--statement by Edward Villella in its final paragraph.