Trouble Cleaning Seats

I decided to clean my gray cloth seats using my carpet cleaning machine (hose attachment where you squirt water/soap mix and then vacuum it out).  My wife drove the car for years hauling our three kids around when they were younger, and they spilled drinks, etc. over the years.  There aren't any real big ugly stains, just sort of lightly soiled mainly on the seat bottoms.
 
The machine sucked out a lot of brown, dirty water so I kept it up until the water turned clear and the cloth was a clean gray color. The next day, I notice general "browning" of the upholstery (where I shampooed), so I attack again with the carpet vac.  I get some more brown water (less than before) and again continue until clear.  Next day, same thing! (general browning of the cloth) I did this a few more times and am now sick of it!  Is there some chemical/preservative in the foam or fabric I am moving around, or is this just old apple juice or something that I'll need to keep sucking out until I get it all?  It is like I clean the surface, and then some more migrates to the surface overnight. There is no odor, it just looks like the cloth was brushed with coffee or something.    

Since the car is eight years old I think you are going to continue to draw 8 years of crap out of the seats for a while. Have you tried a presoak with something like Folex? Tried a steamer on the seats then vaccuum? If nothing works hire a company that will do them several times with a professional extractor.

Thanks for the tips.  I'll keep trying.