Odd iodine test tube

The halogens, being non-polar molecules, dissolve readily in non-polar hydrocarbon solvents. They only dissolve sparingly in the polar solvent, water. Consequently, on adding the hydrocarbon solvent most of the halogen becomes dissolved in it rather than the water. However, the test tube on the right contains potassium iodide solution and the colour of the iodine appears darker in the aqueous layer. The purple colour appears lighter in the hydrocarbon solvent. This is because whilst iodine is only sparingly soluble in water it does dissolve quite readily in potassium iodide solution. So more iodine remains dissolved in the aqueous layer and less transfers to the hydrocarbon layer. Hence, the difference in colours observed.