I got lucky and bought a tube of the Parchment oil paint before it went off of the market. The pigments listed on the back are yellow iron oxide, titanium dioxide and lamp black.
I've had some success mixing Yellow Ochre and Lamp Black into Titanium White to give it just the slightest greenish tint.
Hope this helps.
Craig
PS: I think that John's suggestion of Raw Umber is worth trying. Especially if you have the greenish tint version of the RU.
You want to make Parchment; here's how to do it:
Titanium White, Yellow Ochre and a little Mars Black. This will give you the Liquitex Parchment you are looking for.
*Thanks to Guy Herrick, I finally was able to make this reply.