One version of the ancient epic of the warrior Gilgamesh includes a description of distant mountains that has been translated as
And see! they change their hues incarnadine
To gold, and emerald, and opaline;
Swift changing to a softened festucine
Before the eye. And thus they change their hues
To please the sight of every soul that views
Them in that Land.
Ishtar and Izdubar, translated by Leonidas Le Cenci Hamilton, 1884. (Izdubar is a nineteenth-century misreading of Gilgamesh, due to confusion about the meanings of cuneiform symbols.)
Obviously enough, festucine is a colour, though not one that often appears on colourists’ charts. That might be because nobody is quite sure what hue it really represents. As it is from Latin festūca, a straw, it seems reasonable to argue that it’s a yellowish colour — some reference books indeed assert that it is. But as festūca was also applied to any grass-like plant, others suggest it’s a greenish colour or one partway between green and yellow.
It was invented by the physician and author Sir Thomas Browne in his 1646 encyclopaedic work, Pseudodoxia Epidemica. He certainly meant by it a shade of green: “Herein may be discovered a little insect of a festucine or pale green, resembling in all parts a Locust, or what we call a Grashopper.”
It’s been used rarely. I was startled to come across this example in an old newspaper, an extended high-flown essay on a visit of a blue jay to a local park, whose prose, however purple, doesn’t include it as a colour term:
It looked upon the gazing throng and with abandon cast down the festinative fervor of its song, that festucine song, thin as the reddening sting of ripe wine and as elfinly vivacious as the querulous flight of oriental melodies maddened by the flame of hashish or intoxicated by the love-hungered stress of lutes.
Hagerstown Mail (Maryland), 10 Oct. 1902. Festinative isn’t in any reference work that I’ve consulted, but festinate and its relatives mean hurried or hasty.
These days, festucine is best known among biochemists; it’s the name of an alkaloid. It was extracted by S L Yates and H L Tookey in 1965 from a fungus growing on a grass called tall fescue, botanical name Festuca arundinacea, which demonstrates that fescue is ultimately also from Latin festūca. I guess that their festucine was inspired by the plant’s botanical name rather than its colour.