The temperature of a flame from a known material can be estimated based on the flame's color. However, flame color is also affected by the material being burnt and differs based on its chemical properties in addition to its temperature.
In a typical fire, such as the flame on a candle, the hottest part of the flame is blue. As the flame cools, usually as it moves away from its source, the temperature lowers, and the color goes from blue to yellow to orange and, finally, to red at its coolest point. Color can only be used to estimate the temperature of a flame when the chemical properties of the material being burnt are known.