didfal, again you gotta check references on the particular airplane you are modeling. Tell me what it is and I can do some research for you, as I have a lot of material on Japanese stuff, especially the Zero. In any case, the back of the blades will be in some flat dark color to reduce glare. The fronts of the blades will depend on whether you want to be seen or not. So, in the beginning of the war when the Japanese were dominant, the flash from a polished prop was no big deal. Later on, when it became prudent to be somewhat less conspicuous, the dark paint reduced reflections. Plus, unless you continually polish on a bare propeller, it quickly corrodes, and paint slows that process down.