The colorless technology has been offered as a solution to decrease the cost in wavelength-division multiplexed passive optical network (WDM PON). The self-seeded reflective semiconductor optical amplifier (SS-RSOA) based on WDM PON has been proved to be a promising solution among colorless operations. In this paper, the principles, transmission limitations, and recent research of SS-RSOA based on the WDM-PON technology are reviewed. This paper aims to provide a broad perspective on the status of the SS-RSOA technology to researchers and application engineers who work with solutions in colorless operations. A list of more than 60 research publications on the subject has also been appended for a quick reference.