Here's the one I did for my P-51D skins a year or so ago.   You can see my progression from a darker, duller metal to lighter and shinier.  
Click for full-size version
I intend to fill in the blank with "Punky II" from the 339th FG someday - its got a red & white checkered nose band, red & white spinner, and a green rudder, and fills in a missing FG from the '51D stable.  I have a couple more in mind but there are so few slots left.   Doesn't seem right to fill it up completely.