(from the Latin rubrica, “red ochre,” or “vermilion”). An ordinance or law was by the Romans called a rubric, because it was written with vermilion, in contradistinction to praetorian edicts or rules of the court, which were posted on a white ground. (Juvenal, xiv. 192.)
“Rubrica vetavit” = the law has forbidden it. (Persius, v. 99.)
“Praetores edicta sua in albo proponebant, acrubricas [i.e. jus civile] translalerunt.” —Quintilian, xii. 3, 11.
“Rules and orders directing how, when, and where all things in divine
service are to be performed were formerly printed in red characters
(now generally in italics), and called rubrics.” —
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894