Solution:

The color change in the heated iron from dull red to reddish yellow to white hot can be explained using Wein's Displacement Law. This law states that the wavelength (\(\lambda_{max}\)) at which the maximum emission occurs is inversely proportional to the absolute temperature \(T\) of the object:

\[
\lambda_{max} \propto \frac{1}{T}
\]

As the iron's temperature increases, the peak wavelength of emitted radiation shifts toward shorter wavelengths (from red to yellow and eventually to white, which is a combination of all visible wavelengths). Thus, the observed color change corresponds to an increase in temperature, with shorter wavelengths being emitted at higher temperatures.