Good Flame vs. Bad Flame
One quick way to tell if a natural gas appliance is getting enough oxygen and is adjusted properly is to check the color of the flame on the pilot light.
A pilot or burner flame light should be about 90 percent blue . A yellow flame indicates the appliance isn't working right and could be giving off harmful fumes - have it checked by a service technician right away.
Keep in mind that not all problems with gas appliances will have the symptom of a yellow pilot light - and not all pilot lights are visible. Look for excessive ash or soot around a pilot light opening or air ducts, lengthy "warm-up" times and strange noises or odors.