Two-color emission was observed in three-layer heterostructure organic light emitting transistors (OLETs). These devices consisted of a light-emitting layer made of tris(8-hydroxyquinolinato)aluminium (Alq3) doped with 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM), sandwiched between hole and electron transport layers made of α,ω-dihexyl-quaterthiophene (DH-4T) and α,ω-diperfluorohexyl-quaterthiophene (DFH-4T), respectively. Ambipolar transfer curves were recorded from the fabricated devices, and two-color emission (red and green) was observed during transfer curve acquisition. Red emission was observed to take place at bias conditions supporting hole transport, while green emission occurred when electron-based current was dominant. Moreover, red emission originated from the Alq3:DCM layer, which was verified by comparing the measured spectrum of OLETs to that of corresponding Alq3:DCM organic light-emitting diodes (OLEDs). To investigate the origin of green emission, OLETs were fabricated without an electron transport layer. No green emission was observed, while red emission remained unchanged. Moreover, single-layer transistors and diodes fabricated from DFH-4T expressed green color emission similar to that of three-layer heterostructure OLETs. Therefore, we suggest that green emission originates from the electron transport layer.