The organic light-emitting field-effect transistor (OLET) provides novel aspects for modern organic optoelectronic applications. In particular the full control over the position of the recombination region within transistor channel appears to be one of the most exploitable properties of OLETs. In this thesis this property was used to realize OLETs with voltage-dependent emission colour. The first approach contains an OLET with colour tuneable light emission whereby the emission colour can be defined by the vertical position of the recombination zone and thus by the applied voltages. The device is realized by a parallel layer stack of two ambipolar acenes with different optical and suited electrical properties. Once the transistor is switched from the unipolar to the ambipolar regime a shift in the emission maximum of 50 nm is achieved. The position of the recombination zone is vertically moved through the layer stack and depending on the material the emitted light is either red or green. The second approach contains the combination of an efficient OLET with an independent colour conversion layer on top of the transistor. The colour conversion is achieved by mixing of the transmitted light from the transistor channel and the reemitted light succeeding the photo excitation of the conversion layer at longer wavelength due to a material specific Stokes shift. As the semiconductor and the conversion layer do not need to match electronically an optimized ambipolar transistor setup in terms of carrier transport and quantum efficiency can be chosen. A bottom-contact top-gate transistor with F8BT (poly(9,9-di-n-octyl-fluorene-alt-benzothiadiazole)) as the bipolar semiconductor was chosen. To achieve a colour shift of the emitted light, rubrene was evaporated on the F8BT transistor partially covering the channel. As the absorption spectrum of rubrene matches the emission spectrum of F8BT a colour change can be expected once the rubrene layer is excited via the F8BT emission.