Why does grease turn white when it cools?

Pretty simple -- It's white to begin with, before it melts into the clear liquid and it then re-solidifies.

http://www.cookingforengineers.com/article/110/Bacon-Part-II

Actually, cooking oil is not a clear liquid but a yellowish-gold color.

https://en.wikipedia.org/wiki/Cooking_oil

When the oil cools, it changes its physical state, just as transparent water changes into more opaque ice when it freezes. Understand in its liquid state it is termed an "oil" and in its solid state it is termed a "grease." Because of its molecular structure, it cannot quite form a crystalline structure. Instead, it forms "amorphous regions" and "partial crystals." These irregular areas scatter white light and make the grease appear cloudy. Incidentally, parafifins like candle wax behave just like grease: They are clear in the liquid form and cloudy in the solid form.

ehow.com/about_4596488_cooking-grease.html no longer exists