A pilot light on a gas-burning appliance should be blue. Another flame color, especially yellow, means the appliance's gas-to-air mixture is unsafe and needs to be checked.
When natural gas burns, energy is released in the form of heat. Three things are required for this process to work correctly and safely in an appliance: a pilot light, the right amount of fuel, and the right amount of air, according to the Pacific Gas and Electric Company.
Appliances are carefully adjusted to provide the correct mixture of gas and air. A normal flame should be blue, steady and cone-shaped. The Riverside County Fire Department says a pilot or burner flame should be about 90 percent blue. Flecks of orange are okay, according to Pacific Gas and Electric Company. However, "if the flame is yellow, large, and flickering the appliance may need a safety adjustment."
Decorative gas appliances such as fire logs are designed to have a yellow flame.
It used to be that a pilot light burned constantly, but in some newer appliances, the pilot light is a spark that occurs only when you turn on the appliance.
A slight odor of natural gas means a pilot light may have gone out, according to the Pacific Gas and Electric Company.
If natural gas is burned without enough air, it may produce carbon monoxide, a poisonous gas. The Louisville Gas and Electric Company says that a person exposed to carbon monoxide "may complain of dizziness, headache, nausea, fatigue and other flu-like symptoms."