As indicated above, steps 1 and 2, commonly referred to as the Landolt and Duchman reactions respectively, are dominant so long as HSO_{3}^{-} is in excess. Once it’s consumed, step 3 can no longer occur and an appreciable concentration of I_2 becomes present. The starch indicator then rapidly combines with the iodine (triiodide, I_{3}^{-}, is actually present as well, in equilibrium with I_2 and I^{-}) to form the signature, deep blue, iodine-iodide-amylose complex (John A. Church and Sanford A. Dreskin, 1968). One can easily see that color development will not occur if the molar ratio of HSO_{3}^{-} to IO_{3}^{-} is greater than 3:1, because HSO_{3}^{-} must not be in excess. For more information on the chemistry behind the color development itself, check out my previous citation.