A strategy is developed to modulate the fluorescent color of carbon nanodots (CNDs) through regulating photon reabsorption and carbonization degree. On the one hand, the emission color is tuned through enhancing the photon reabsorption via the concentration increase. Essentially, the emitted photon of short wavelengths is supposed to be reabsorbed by a neighboring CND, subsequently resulting in a photon emission of long wavelengths. On the other hand, by reaction time control, a higher carbonization degree of CNDs is obtained, which renders larger sizes and less oxygen related groups of CNDs, giving rise to narrower bandgaps, e.g., emissions of longer wavelengths. Through cooperatively managing the carbonization degree and photon reabsorption, a single ultraviolet light can be converted into multi-color luminescence across the entire visible range by using our one-pot-pyrolysis CNDs.