Amylose molecules consist of single, mostly unbranched chains of glucose molecules, shaped like a spring. It is speculated that the iodine (in the form of I5- ions) gets stuck in the coils of the beta amylose molecules (soluble starch). The starch forces the iodine into a linear arrangement in the middle groove of the amylose coil. There is some transfer of charge between the starch and the iodine. This changes the electron arrangements and hence the spacings between energy levels. The new spacings absorb visible light selectively and give the complex its intense blue color.