Navy bombs, such as on the Val, were a light grey with a green nose band. Some were just all grey. I don't know about FS numbers for I never use them. Any light grey, such as neutral grey should be sufficient. Here's a good reference.
http://www.clubhyper.com/reference/japanesebombsdw_1.htm
Paint the propeller and hub Aluminum and the back side of the blades flat black for a Pearl Harbor Val...
Good luck,
Joe