The colour of the flame of combustion depends on the carbon compound being used. We will get a clean flame with saturated hydrocarbons while unsaturated carbon compounds will produce a yellow flame with black smoke. Ultimately, the burning of carbon compounds results in a sooty deposit on the surface. If there is incomplete combustion of saturated hydrocarbons due to limited supply of air, a sooty flame will be observed. A lot of carbon remains unburnt due to the high concentration of carbon, which escapes as small particles called soot.