Why does olive oil change colour when frozen?
Olive oil is made up of many different compounds, including different types of fats, vitamins and minerals and waxes. Each of these elements will become solid at different temperatures so when olive oil is put into a freezer they will all freeze at different rates. This tends to cause cloudiness in the oil and this makes the oil look paler in colour. However when the oil thaws the compounds return to their original liquid state and become clear again. Olive oil is not usually harmed by freezing.
Olive oil will also tend to change colour over time due to exposure to the air (oxidation). It can become paler in colour and milder in taste, though is usually still safe to eat. This change can be accelerated if the oil is stored in direct light or in very warm conditions so if possible store your olive oil in a dark place with a cool, but not cold, temperature.