If you noticed that your gas range has a yellow or an orange flame instead of the standard blue flame with a yellow tip in the center of the flame, it might be due to the following factors:
WARNING: Before working on any appliance, make sure that all power (electricity) and utilities (water and gas) have been turned off and/or disconnected on the appliance. 

1) Make sure the burners are clean and placed correctly. If  you have an orange or yellow burner flame on your gas range make sure the burner portholes are clean and free of debris. Spillovers and cooking grease can block these openings which can affect the flame color. Make sure the burner holes and igniter are clean and free from any debris. Use an old toothbrush to clean these areas. If you take the burners apart to clean them, make sure you place them back in their proper position. This can also affect the flame color on your range.

2) Do you have the proper orifices for your burners? Be sure you are using the proper orifices depending on whether your range uses liquid propane (LP) or natural gas. Was your range converted from one energy source to another? Along with the orifices, make sure that the gas pressure regulator valve was changed over and the brass orifice that supplies the bake/burner was adjusted. Other adjustments might need to be made depending on your range. Consult your user’s manual for more information.

3) Turn off your humidifier. As strange as it may sound, humidifiers seem to turn gas range flames from blue to orange. Turn off your humidifier to see if this makes a difference in your stove’s flame appearance.

Please note that it’s very rare for a discolored flame to be the result of natural gas quality.

The danger of orange or yellow flames
Orange or yellow flames, or sooty flames, could also mean you have incomplete combustion happening, which could lead to carbon monoxide buildup in your home. There might be an 
air-gas mixture problem, or a problem with the gas pressure to the appliance. If you suspect this, turn off the gas supply to your appliance and leave your home. Contact a qualified gas 
technician or fire department to check it out. 
Remember, you can’t see or smell carbon monoxide, so it’s important to have carbon monoxide alarms placed throughout your home.