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In some societies, clothing may be used to indicate rank or status. In ancient Rome, for example, only senators could wear garments dyed with Tyrian purple. In traditional Hawaiian society, only high-ranking chiefs could wear feather cloaks and palaoa, or carved whale teeth. Under the Travancore Kingdom of Kerala, (India), lower caste women had to pay a tax for the right to cover their upper body. In China, before establishment of the republic, only the emperor could wear yellow. History provides many examples of elaborate sumptuary laws that regulated what people could wear. In societies without such laws, which includes most modern societies, social status is instead signaled by the purchase of rare or luxury items that are limited by cost to those with wealth or status. In addition, peer pressure influences clothing choice.

What country once only allowed their emperor to wear yellow?
China