The present invention provides an optical fiber in which the transmission loss increase is suppressed even under a high-humidity condition or under a water-immersed condition. A colored optical fiber (22) according to an embodiment of the present invention is a colored optical fiber (22) formed by applying a colored layer to an optical fiber (14) including a glass optical fiber coated with at least a double-layered coating layer of a soft layer and a hard layer, and the ratio of thermal expansion coefficient between the coating layer after the colored layer of the colored optical fiber (22) is applied and the coating layer of the optical fiber (14) before the colored layer is applied is 0.87 or more. Furthermore, an optical fiber ribbon (32) according to another embodiment of the present invention is an optical fiber (32) formed by arranging a plurality of the colored optical fiber (22) in the form of a plane and coating them all together with a ribbon resin and the ratio of thermal expansion coefficient between the coating layer after the colored layer of the colored optical fiber (22) is applied and the coating layer of the optical fiber before the colored layer is applied is 0.90 or more.