Here's why:

* Iodine's Properties: Iodine is a nonpolar molecule. It has a deep purple-black color in its solid form.

* Decane's Properties: Decane is a nonpolar alkane hydrocarbon.

* "Like Dissolves Like" Principle: Nonpolar substances tend to dissolve in other nonpolar substances. This is because the intermolecular forces between similar molecules are stronger.

* Color Change: When iodine dissolves in decane, the iodine molecules are surrounded by decane molecules. This causes the iodine to change color from its usual solid form to a violet solution.

Important Note: The color of iodine solutions can vary slightly depending on the concentration of iodine and the type of solvent used.