The characteristic ammonia-like odor will be replaced by a musty odor. Spots caused by urine may be a dull yellow or even red. Plant Foods and Fertilizer Spills of some liquid plant foods or leakage from house plants can cause color changes in carpet. Spots of this kind usually develop near the backing and progress upward through the pile to the surface. Stains of this type may not be apparent for months.
Spots are usually dull yellow in color.
Some pesticides and insecticides can cause discoloration or color loss of carpet. Chemicals may cause fading around baseboards when spray is directed to the carpet instead of the baseboard, or when spray is applied to household plants. Follow label directions and spray only when necessary. Protect the carpet with drop cloths. A greater potential for color change exists with repeated applications.