Why iodine is brown in alcohol and aceton but violet in impolar solvents?

Iodine reacts with polar solvents, such as alcohol, much differently then with nonpolar solvents. Since you don't have a specific case with nonpolar solvents I'll give you a general answer. Compounds absorb certain wavelengths of light, the wavelengths they don't absorb they reflect. The specific wavelengths that are absorbed are dependent on the types of molecular interactions that are occuring. So iodine in its solid form looks yellow. When you throw it in alcohol it is no longer yellow because of the new interactions. Same thing for nonpolar compounds. I hope that helps