What happens when iodine is added to boiled egg?

When iodine is added to a boiled egg, it reacts with the proteins in the egg white and turns them a deep blue-black color. This color change is due to the formation of a complex between iodine and the amino acid tyrosine, which is present in high concentrations in egg white. This reaction is commonly used as a simple test for the presence of protein in a substance or solution. In the case of a boiled egg, the iodine reaction provides a visual indication of the presence of protein in the egg white.