 Marks of cadency (whether bordures, the marks of the English cadency system, or any other mark), and presumably marks of distinction, can be exceptions to this rule.For example, many members of the French royal house had a red border or bend against the blue field.Also, in Great Britain, cantons added to indicate baronetcy of Ulster ("argent, a hand couped gules") ignore this rule; otherwise they could be displayed by no one with a metal field.