What color should the flames be in a correctly adjusted gas burner?

In a correctly adjusted gas burner, the flames should exhibit a bright blue inner cone surrounded by a darker outer cone. This blue coloration indicates that the gas is burning efficiently and completely, with a proper balance of gas and air. The blue inner cone is the hottest part of the flame and shows that the combustion process is optimal, leading to higher energy output and less soot production.

In contrast, other flame colors can indicate incomplete combustion or insufficient air supply. Bright orange flames typically suggest that there is too much gas relative to the amount of air, which can lead to inefficiencies and soot buildup. Yellow flames with a pale blue inner cone can indicate an imbalance as well, while red flames with white tips generally signify insufficient combustion, leading to a lower efficiency rate. Thus, the bright blue inner cone is a key indicator of a well-adjusted burner, making it the correct choice for this question.