So, I was going to make a long post on how to get the effects of a stain, then I found this:
Here is a link to a great tutorial on how to make a poster in photoshop. In the first part, there is a section on how to create a stain: The rest details a nice parchment look.
Now, you can follow the same steps with a filled selection in photoshop. Basically, in the end, if you follow the dodge/burn tactic, you will get what you need.