Here is my offending stain. Not sure what it is or how it got there. It was nearly impossible to get a good picture of it due to my carpet color/lighting/flash/whatever, but I promise it's right there in the center! Now, on to how to remove offending stain!
Make a mixture of 1 cup ammonia, 1 cup hot water, and put in a spray bottle. Spray the stain until wet.
Place a light colored towel/handkerchief/pillowcase on top of the stain and iron it. Yes, iron it.
Why a light colored cloth? So you can see the stain come off your carpet and be absorbed into the towel!
Tada! Amazing!! I haven't found anything it wouldn't remove yet. It works wonders on pet stains. Now, go clean your carpets!