In a flame, there are four zones:(i)Non-luminous zone,(ii)Luminous zone,(iii)Dark zone and (iv)Blue zone
the yellow or orange color that you see in the fire is in the luminous zone. The color occurs due to the partial combustion of the substance. This zone is moderately hot. If you see an orange or a red color in the flame it means that the substance that the substance which is burning has a lot of impurities.