We demonstrated a monolithic white light-emitting diodes (LEDs) epitaxial structure with blue, green, and amber emissions by introducing the blue InGaN/GaN five quantum wells (QWs) and InGaN/GaN single quantum well (SQW) with In-phase separated green/amber emissions as an active layer. Three wavelength emissions were developed by increasing the thickness of InGaN SQW grown on blue InGaN five QWs. From high resolution transmission electron microscope, In-phase separation was clearly observed in a 3.5-nm-thick InGaN SQW. In-phase separation would be generated by the spinodal decomposition which was promoted by the composition pulling effect related to the increment of well thickness. Therefore, white lighting LEDs with three wavelengths for blue emission from InGaN/GaN five QWs and green/amber emissions were achieved by the In-phase separation in InGaN SQW.