The answer to 'air duct discolored' is that discoloration in air ducts is typically caused by a buildup of dust, dirt, and debris over time. Symptoms may include visible staining or darkening of the duct material, as well as reduced airflow and air quality. The best solution is to have the air ducts professionally cleaned by a licensed HVAC technician.
Attempting to clean air ducts yourself is generally not recommended, as it can be difficult to fully remove all the accumulated contaminants and may even cause further damage. Professional duct cleaning services have the specialized equipment and expertise to safely and effectively clean your entire duct system, restoring airflow and improving indoor air quality.