Carl's got some ideas meriting a trial 'rub' on some raw steel. Maybe an old frame or fork you could test some recipes on?
The other thing I was thinking was, do your Jade, then try 'subduing the color' by using Rustoleum's Satin Strawflower (a very muted yellow shade, almost bone color) or the Fossil (really muted shade of green) which I used last year on One-Liner.
It's a very light dusting, sprayed from about 3-4' away, and not full coverage. And as always, 'stop before you think you are done'. What it does is mute the original color so it's not as deep, like it's been fading in the sun for a few decades.
If you want to add some rust-ification, the ol' Rustoleum Multi-color Texture paint, in your color scheme, probably the lighter brown, around the welds and tops of the frame tubes can add that quality. Then rub down lightly with steel wool or leave nubbly, whatever feel / look you prefer.
but still makes me want to put a plate on the seat for a picnic 
