The vintage cap in my photo is from the Internationals card I had for Christmas in 1979. As Mark has mentioned above, the roundel is a sticker rather than painted.
I think that the roundel - and the diamond that it's stuck to - was painted on the Cotswold version of this field cap. I don't have a Cotswold DAK cap, but I do have their green one and it's virtually identical to both caps, except a bit more detailed in its painted state.
Colour-wise, I seem to recall that the Cotswold cap might have been manufactured in a shade that was somewhere between the two caps I've shown in my picture.
Another feature of the caps pictured above is that the vintage one feels a little "less thick" than the 40th one.
I hope that helps.