I knew I've seen this somewhere before.
Are you having an issue with the carpet or the mats? I think is the carpet if I read correctly (scratch)
Extracted from Wiki
If you drive in a cold climate, you'll very likely end up with white stains on your car's carpeting from road salt. Fortunately it's easy, if a little repetitive, to get the stains out. Here's how.
Steps
1. In a spray bottle, mix up a solution of 1/2 warm water and 1/2 white vinegar.
2. Spray the stained area with the solution.
3. Press a dry terrycloth towel over the wet area.
4. Remove the towel when it's soaked.
5. Repeat until the stains are gone.
Tips
* If you don't want to spend a whole day doing this, apply the solution whenever you happen to be driving. Just remember to remove the towel promptly and let the carpet dry out.
* Don't be discouraged by a deep-rooted stain. It will come out eventually.
Warnings
* Avoid the temptation to rub the stained area. It doesn't help and may damage the carpet.
Alternatively, if you use a foaming carpet cleaner from an auto store, you can use the soft plastic brush they provide to work in the solution. It will cleanse the area.
Source:
http://www.wikihow.com/Get-Salt-Stains-out-of-Your-Car's-Carpet
Note: Yes, the OEM all weather floor mats are really good