Some red, some blue. In the Common Law, red bags are reserved for Q.C.'s and Sergeants; but a stuff-gownsman may carry one “if presented with it by a silk.” Only red bags may be taken into Common Law Courts, blue must be carried no farther than the robing-room. In Chancery Courts the etiquette is not so strict.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894