The realization of efficient red, green, blue (RGB) light emission can be achieved by covering a blue light emitter with color-converting dye/matrix layers. We present theoretical calculations and experimental data of an electroluminescence device based on parahexaphenyl, an organic semiconducting material, which emits bright blue light when used as an active layer in a thin film device. The waveguiding effects in the various layers making up the RGB device are investigated in order to maximize the brightness, and optimize the angular light intensity distribution of the external emitted light. Quantum efficiencies (QE) for green color conversion of 48&percent;, and red conversion of 13&percent; from blue emission were determined by calculating over all emission angles and confirmed by experimental QE measurements. The efficiency can be drastically improved when the device layers are directly coupled to each other by refractive index matching, where color-conversion efficiencies of 90&percent; for blue to green and 80&percent; for blue to red can be achieved. ©1997 American Institute of Physics.