Champagne is (to me) a pale yellow so I'd put just a dot of yellow in there and maybe a tiny dot of brown.
Did they give you a sample of the color? That invite looks brown to me.
Just be sure to add tiny bits of color as that shade is sooooooo light you don't want to over do it. You can always knead inmore but can't easily lighten it if you get it to dark.
maybe a little ivory and a tiny tiny bit of yellow
I agree with cathie.
I've had to do champagne before and thats what I did,turned out perfect.
The invite does look kind of khaki, did it scan dark or is that the color?