Unsaturated hydrocarbons usually produce:

Unsaturated hydrocarbons have a higher carbon-to-hydrogen ratio compared to saturated ones. During combustion, there isn't enough oxygen in the air to burn all the carbon completely. This incomplete combustion produces unburnt carbon particles, which glow yellow and appear as black smoke. Saturated hydrocarbons typically produce a clean blue flame due to their lower carbon-to-hydrogen ratio and a higher percentage of hydrogen.