The answer to 'why is my paver yellowing' is that pavers can yellow over time due to a few common causes. This is often caused by exposure to UV light from the sun, which can break down the materials in the pavers and cause them to lose their original color. Another common cause is mineral deposits or efflorescence, which can leave a white or yellowish haze on the surface of the pavers.
If the yellowing is mild, you may be able to clean the pavers yourself using a specialized paver cleaner or a diluted bleach solution. However, for more severe or persistent yellowing, it's best to call in a professional landscaper. They can assess the underlying cause and recommend the best treatment, which may involve more intensive cleaning, sealing, or even replacing the affected pavers.