Although there is no "social colour code" that I am aware of, most gentlemen use red sealing wax. In the 18th and 19th century (and indeed, even today) it was not uncommon for a lady to seal an envelope with a different colour sealing wax, often green.

As far as I am aware the wearing of signet rings by ladies is far from fashionable. In grander households a lady would have her own seal (often a desk seal or a smaller fob seal) which would be engraved either with her arms and those of her husband, or perhaps a monogram or cypher of her initials (or those of her title) sometimes surmounted by a coronet denoting her rank.