Simultaneous generation of red (R), green (G), and blue (B) wavelengths in different grating structures of 5% MgO doped domain engineered LiNbO₃ is studied theoretically by employing the type-0 quasiphase-matched (QPM) technique. The spectral output from two cascaded, four segmented, and two-phase shifter (PS) QPM structures using second-harmonic generation, difference-frequency generation, sum-frequency generation, and third harmonic generation were analyzed and interpreted. We observed RGB in the range of 620 to 650 nm, 530 to 580 nm, and 430 to 468 nm for red, green, and blue, respectively, for various configurations of input wavelength, period, device length, segment length, location, and width of the PS domain. The influence of the input pump, operating temperature, pump detuning, PS width, and phase matching periods are analyzed for all the proposed schemes. Fluctuation in the output wavelengths of about 10 to 20 nm was observed due to the temperature variations from 25°C to 150°C in steps of 25°C. Further, the advantages of using a MgO-PS QPM structure over the other proposed schemes have also been addressed for their potential application in a laser-based projection display system.