The color of the eastern sky just before sunrise. Coined by wordFrank Sinatraword, who certainly saw enough of it.
"Look at the colors!" he would say, pointing bleary comrades toward thousands of sunrises. "What kind of blue would you call that?" He called the tint of sky that offered him most peace Five O'Clock Vegas Blue. "You have to see it to know it." (from The Way You Wear Your Hat, by Bill Zehme)