The brightest part of a flame is called the inner core or the luminous zone. This region appears brighter due to the high temperatures and the presence of incandescence, where solid particles in the flame emit light as they get heated. The inner part of the flame, which is generally blue in color, is hotter and contains unburned gases along with the main combustion reaction, while the outer part or the outer envelope tends to be cooler and less luminous. Flames produce varying colors depending on the materials being burned and oxygen supply, influencing the brightness of different sections.