I built this one a while back. I don't remember using any gray myself, and though I use Tamiya for a lot of projects now, I hadn't come across any yet when I was painting my B'rel and used MM enamels. If you're interested and anyone knows ratios to mix Tamiya colors to match, here's what I used:
Green plating: varying pattern of FS Pale Green, Green Zinc Chromate and Willow Green
Orange "feather" details: Russian Marker Red
As I said, it was a looooong time ago and I hadn't messed with washes yet. Sadly, the kit was lost between moves so I can't send pics.
Maybe it's time I replaced the old bird...