The dorsal fur of Oligoryzomys flavescens consists of bright orangish-brown hairs mixed with blackish hairs, the hairs on the flanks are all orange and the underparts are yellowish-grey. The boundary between the upper parts and the underparts is indistinct, grading from one colour to the other.
The description highlights the specific coloration and blending of fur in Oligoryzomys flavescens, emphasizing the gradual transition between upper and lower parts of the coat.