Defects in the dye inherent in manufacturing can come from a failure of the dye to attach to the fiber. Such problems can occur on nylon that has been dyed with basic or cationic dyes. The white yarns below were soaked for four days in an alkaline detergent designed for carpet cleaning. The result was a total color loss.

Fume fading is a form of color loss along the edges of walls, around the edges of drapes, and down the edges of stair. The photo below is of a rose colored carpet that is turning green from fume fading.

Fume Fading

Defects in the dye

Bleach will make spots that are lighter than the surrounding carpet, with irregular edges. Mixing hydrogen peroxide and acidic acid will make per-acidic acid that can also destroy the color of the carpet. 

Sun light fading will occur gradually on the west or southwest side of a structure or near large windows. Whether or not it can be called an acceptable defect depends upon testing. The picture below is of a door mat kept next to a sliding-glass-door that has been laid onto an unaffected section of carpet.

Sun Fading

Bleach