The chocolate-brown colour is caused by the active ingredient povidone-iodine and is typical of iodine preparations. You may already be familiar with this property from wound disinfection with iodine-containing solutions or ointments. Incidentally, povidone-iodine is also one of the most widely used active ingredients in gynaecological operations worldwide. So, the colour is only due to the iodine and does not affect the quality of the medicine.