Symbolism, Imagery, Allegory
Poor Malvolio. When he decides to wear a crazy get-up that involves yellow stockings (hosiery for men) with cross-garters, his silly costume becomes a glaring symbol of his social ambition and foolish desire for power. His yellow stockings are a lot like the "rich jewel" he fantasizes about stroking in Act 2, Scene 5 (see "Jewels" above). Huh? Let us explain.
Malvolio, as we know, is duped into wearing the completely inappropriate and unfashionable duds when he reads Maria's forged letter. The letter tricks Malvolio into believing that Olivia likes yellow stockings and that, by wearing them, Malvolio will be able to win Olivia's hand in marriage, which would launch Malvolio from servant to nobleman. When Malvolio turns up in his silly outfit, Olivia thinks he's gone crazy. It also doesn't help that Malvolio is smiling like a loon and slobbering all over Olivia's hand, which the letter also instructed him to do. The point is that Malvolio is Olivia's servant and, according to Elizabethan attitudes about class and social rank, Malvolio would have to be crazy to think he had a chance with her.
History Snack: There were actually rules (called "Sumptuary Laws") that governed choices in dress. One of our favorite literary critics, Lisa Jardine, shows that fabric, color, and style of costume were all symbols meant to distinguish and separate gender and class identities. It was a big no-no to wear something inappropriate to your social rank. That goes for wannabes like Malvolio and cross-dressers like Viola.
It's funny, though, that Viola's cross-dressing is not punished. Her temporary disguise as "Cesario" actually helps her land a husband. It's also responsible for Olivia's marriage to Sebastian and the play's overall "happy ending." Perhaps this is because Viola is not a social climber like Malvolio. As Duke Orsino points out in Act 5, Scene 1, Viola's "blood" is "right noble."
Still, there's more to say about Viola's "Cesario" disguise. The fact that Viola is so convincing as a pretty boy servant tells us that gender and class identity can be impersonated and performed. (It happened just about every day on the Elizabethan stage, after all.) While Malvolio's inappropriate costume change is unsuccessful, Shakespeare goes out of his way to leave Viola on stage at the play's end in her male attire. Check out "What's Up with the Ending?" for more on this.