“507. All Cats are alike grey in the Night.”
Introductio ad prudentiam: Part II (1727), Gnomologia (1732)
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Thomas Fuller (writer) 420
British physician, preacher, and intellectual 1654–1734Related quotes

“I am the cat who walks by himself, and all places are alike to me.”
The Cat that Walked by Himself.
Just So Stories (1902)
Source: The Cat That Walked By Himself

“In the night all cats are gray.”
Source: Don Quixote de la Mancha (1605–1615), Part II (1615), Book III, Ch. 33.

“Night's black mantle covers all alike.”
First Week, First Day. Compare: "Come civil night,… with thy black mantle", William Shakespeare, Romeo and Juliet, act iii. sc. 2.
La Semaine; ou, Création du monde (1578)

When all candles are out, all cats are grey,
All things are then of one color, as who say.
And this proverb faith, for quenching hot desire,
Foul water as soon as faire, will quench hot fire.
Part I, chapter 5.
Proverbs (1546)

Part I
The City of Dreadful Night (1870–74)

“Grey and grey and grey and grey”
Lyrics, Misc.

The Prisoner of Chillon http://readytogoebooks.com/PC31.htm, st. 1 (1816).