For General Nylon Carpet spotting almost all spots can be removed if gotten to immediately.

Wet Spot:

A new carpet wet spot on the carpet should be blotted with white terry towels then wetted with water and blotted again do at least three times so you wont see a remnant of the carpet spot. Use carpet spotting guide for inks and spots that may bleed.

Pet Spot:

A fresh pet spot on the carpet should be attacked the same as a wet spot but applying an enzyme to the carpet afterwards. The application of an enzyme such as, "Kids n pets" or "Natures Miracle", removes any remaining contamination that might of soaked into the carpet. This is annoying to do but remember your saving thousands of dollars of carpet and no one can do as completely as you at the time of the accident. We had a new puppy and knowing this procedure and using my commercial enzyme we got no pet odor or stains...and I never got out my truck mount.

Dry Soil:

if a powder is spilled on the carpet vacuum only to remove they may cause staining or bleaching when wetted.

Look of carpet spot

If a spot is grey-black it probably is a soil that a commercial spotter could be used for such as: "Folex Carpet Spot Remover". Be careful when using spotters because soap re-attracts soil. So if a spot comes back after it was gone it may be soil sticking to the soap and it should be rinsed out with water not re-soaped up.

Browned areas require special low ph chemicals as do rust and I would recommend you call me or another professional for these.

More complete spotting guides:

I have a link to some user spotting guides if you want to try to remove a more complicated spot yourself but I cannot be responsible for accuracy of the guide or results from using them.

Stain Removal Guide for Carpets - Stainmaster

CRI Guide