A correctly working stove burning methane gas has blue flames. Flames with yellow, orange, green, purple or red coloring indicate an issue with either the stove or gas supply.
A yellow flame caused by too little oxygen does not reach the same temperature as a blue flame. Adjusting the burner's air shutter corrects this issue. Orange, green, purple or red flames indicate presence of rust, dust, oil or gases other than methane in the gas supply. The colors of the flames are most obvious in a dark room. Examining the flame color of a gas stove can detect issues before the stove becomes unusable.