How to get stain out of carpet?

We have a very long path from the front door on one side of the house through the Living room and hallway up to the master bedroom door. I'm assuming its a walking path stain. If tried viniger, dawn, bakingsoda, carpet cleaner an just about every pre treatment spray an it won't go back to its normal color.... show more We have a very long path from the front door on one side of the house through the Living room and hallway up to the master bedroom door. I'm assuming its a walking path stain. If tried viniger, dawn, bakingsoda, carpet cleaner an just about every pre treatment spray an it won't go back to its normal color. Is their anything else I can try? The carpet is only 4 years old so I know it can't be worn down already.
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