A directly modulated, colorless, weak-resonant-cavity Fabry–Perot laser diode (WRC-FPLD)-based transmitter is, for the first time, proposed and experimentally demonstrated for wavelength-division multiplexed passive optical networks (WDM-PONs). The transmitter utilizes optical gain-saturated reflective semiconductor optical amplifier (RSOA)-induced feedback and is free from external optical injection. Experimental investigations are undertaken of the impact of RSOA-feedback dynamic mechanisms on directly modulated output optical signals and corresponding colorless transmission performances for various system architectures. It is shown that the coherent-like optical source produced by the proposed transmitter architecture offers an output wavelength tunable range as large as 65 nm with side-mode suppression ratios (SMSRs) of >37 dB. In simple 25-km single-mode fiber intensity modulation and direct detection WDM-PON systems, the colorless transmission of directly modulated 7.5-Gb/s optical orthogonal frequency-division multiplexed signals is experimentally achieved over a wavelength tunable range of 35 nm, during which <1 dB differences of received optical powers at bit error rates of 2.3×10−3 are also experimentally obtainable.