The answer to 'sprinkler system yellowing' is that it is usually caused by mineral buildup or chemical imbalances in the water. This can lead to discoloration and staining of the sprinkler heads, pipes, and surrounding areas. The symptoms may include yellow, orange, or brown stains on the sprinkler heads, grass, or pavement.
To address this issue, you can try flushing the system, adjusting the water treatment, or replacing any heavily stained components. However, if the problem persists or you're unsure of the cause, it's best to call a professional landscaping or irrigation technician to diagnose and resolve the issue.