X: A symbol (Sept 10th 2010)

Identify X in the quote below.  The picture above is related to X.

"As for the X's famous color, __, it was not an obvious choice. Mr. Starr reports that Ammann favored gray (as used for the __), and others wanted black. While the Navy “preferred a yellow and black striping to facilitate visibility __ through low-lying fog,” the Army Air Corps wanted a red-and-white color scheme more visible from the air. The __ paint was primer, used to protect __ against the elements, and it gradually went from being a default choice to the color of choice.

In an over-the-top burst of purple prose, Mr. Starr observes that __ not only “unified the __ into one compelling statement,” but also summoned memories of “the gold of the __ that had created the __, and the gold of the Golden Horn of the Bosporus first suggested by John Frémont when he named the site in 1846 and by metaphor evoked a color-drenched city of towers, domes, and stepped-back structures rising like Constantinople from blue waters along green hillsides, their red-tiled roofs touching a sun-flooded azure sea.”"

(Michiko Kakutani; New York Times Book Review Aug 23, 2010).