When coconut or other oils are melted, they turn into a liquid, which you can easily see through. However, when they cool and solidify, the fatty acid molecules begin to come together and crystallize. Think about how you can see through liquid water much better than you can see through ice, which gets cloudy because of the water crystals.
By cooling something more quickly, you can reduce the number and size of the crystals that form. Ice that is frozen very quickly is less cloudy. Similarly, if you want your coconut oil to remain more smooth, you should cool it very quickly by putting it in the back of the refrigerator.