Vestidos largos morados, or long purple dresses, are appropriate dresses for either the guests or the guest of honor at a quinceañera. Traditionally, girls who are honored with a quinceañera on their 15th birthday wear ballgowns of any color, and their guests also wear formal wear.
Female guests at a quinceañera are typically choose a little black dress or even a maxi dress, while men usually wear a suit or tuxedo. The right outfit should be age appropriate and fit well. If either the guest of honor or her guests dress in clothing that's too tight, too baggy, too old or too young, they may not feel comfortable at the party.