You may not notice this, however, since it can happen very gradually over moments.
Bleach, hair dye, drain cleaner, some insecticides and certain other household items will most likely cause permanent color alterations in the carpet that shouldn't be reversed with any cleaning methods. http://bilbray.com/__media__/js/netsoltrademark.php?d=Tigaedu.com%2Fblog%2Findex.php%3Fentryid%3D416349