When iodine is added as an indicator to an unknown substance, it typically reveals the presence of starch. If starch is present in the substance, the iodine will react with it and produce a characteristic color change, turning from a yellow-brown color to a deep blue or black color.
If the iodine does not change color and remains brown, it indicates that starch is not present in the substance. This method is commonly used in laboratories to test for the presence of starch in various samples.