Recently I learned what the days of the week are and noticed "kinyobi" 金曜日. I'd like to know where the term "gold" relates to. Were people in ancient Japan paid at Friday each week?
金 in 金曜日 refers to Venus (金星). In fact, "Fri" in "Friday" also refers to Venus, also known as Frige's star. Both are almost certainly derived from the Roman names for the days of the week.
In addition to Zhen Lin's point, it is also worth noting that the Japanese names for the days of the week come from Chinese, and classical concepts of the five elements: fire (火), water (水), wood (木), metal (金), and earth (土), plus the two primary celestial bodies, the sun (日) and the moon (月).
Read more about the classical Chinese five elements in the Wu Xing article on Wikipedia.