Light emitting diodes (LEDs) based on In(x)Gal(1-x)N (x = 0.15-0.2)/GaN multiple-quantum wells ( MQWs) have been grown on sapphire substrates. Their wavelength emission can be tuned from blue to orange by increasing the QW thickness. This opens the way for monolithic white LEDs by combining several QWs of various thicknesses, i.e., "colors", inside the GaN p-n junction. This is demonstrated by the realization of white (blue + yellow) dual color LEDs. The coordinates in the CIE 1931 chromaticity diagram of the EL spectrum are (x = 0.29, y = 0.31) and correspond to a color temperature of 8000 K. The expected performances of the monolithic white LEDs are compared to hybrid technologies such as blue LEDs pumping yellow phosphors.