Carbon nitride quantum dots are important metal free semiconductors due to their controlled optoelectronics and low toxicity. Here the sulphur heteroatom doping of these nanomaterials is achieved by the low cost hydrothermal process leading to a multicolour photoluminescence. A simple change in water/dimethyl sulfoxide ratio as a solvent helps to achieve a wide tunability in photoluminescence, almost from blue, green, yellow to red with a high quantum yield. This change has been accounted for the particle size, bond conjugation, and heteroatom doping of carbon nitride nanoparticles. Due to multicolour emission, benignity and low cost these materials can be the promising candidates for various optoelectronic applications.