Hi Mick.
Are you basing your model off a particular photo? If not, don't get too bogged down with 'what's the right yellow", no one really knows anyhow. Take Australian Leopards for example, in one squadron there would be 16 different shades of green.
My advice would be to experiment with different shades, I tend to start with Gunze Sand Yellow with a bit of Tamiya flesh to fade it out. I prefer to start with a lighter colour so i can darken it with postshading and washes etc.
I hope this gives you some direction.
Willy.