Complex sentence: The summer dorsal pelage and ventral pelage are dark rufous or blackish brown, and the winter dorsal pelage is a grayish brown, slightly lighter in tone than the ventral pelage.
Split into simpler sentences: The summer dorsal pelage and ventral pelage are dark rufous or blackish brown. The winter dorsal pelage is grayish brown which is slightly lighter in tone than the ventral pelage.