Simply looking at the flame, it provides useful information for your interest. Natural gas combustion for instance, in the kitchen, should have a blue color. With the presence of yellow, red or green, they are indications of undesirable factors.
Red indicates the presence of particles proceeding from the conducts, composed by oxidation. Green usually when metals like copper, brass, zinc or others are being part of the combustion. The most common color, the yellow, shows the presence of carbon monoxide due to an incorrect quantity of oxygen. The design of the conducts and oxygen intakes are very relevant in this regard, like the impurities present on them: ash or soot, or some kinds of carbonized elements.
It's useful to know that the flame color tends to be bluer with more oxygen, and without it, yellow, or an alike tonality like orange. As carbon monoxide is toxic, any production source must be checked and solved if it is in a house.
Another factor to know is the importance of the oxidizer to produce more heat in the combustion. So, with the right quantity of oxygen, the same quantity of gas produces more temperature. In other words, it's more efficient.