In 957, scholar Shuang Ji was sent to Goryeo as an envoy, and, with his advice, Gwangjong instituted the national civil service examination in 958, with the goal to expel officials who gained court positions due to family influence or reputation rather than by merit. The examination, based on the Tang's civil service exam and the Confucian classics, was open to all male free-borns to give everyone, not only the rich and powerful people, the opportunity to work for the state, but in practice only sons of the gentry could gain the necessary education to take the exam; royal relatives of the five highest ranks were, instead, left out on purpose. In 960, the king introduced different colours for court robes to distinguish officials of different ranks. The major examinations were literary, and came in two forms: a composition test (jesul eop), and a test of classical knowledge (myeonggyeong eop). These tests were officially to be held every three years, but in practice it was common for them to be held at other times as well. The composition test came to be viewed as more prestigious, and its successful applicants were divided into three grades. On the other hand, successful candidates on the classical examination were not ranked. In the course of the dynasty, some 6000 men passed the composition examination, while only about 450 passed the classics examination.