all cats are gray after dark/at night

Without sufficient knowledge one cannot distinguish between alternatives. This assertion appeared in numerous proverb collections, beginning with John Heywood’s of 1546, where it was put, “When all candels be out, all cats be grey.” A still older version, dating back some 2,000 years and stated by the Roman writers Ovid and Plutarch as well as by later writers, had it that all women are the same in the dark, a view now disputed by all but the most hardened misogynists.