The answer to 'retaining wall installation yellowing' is that the most common cause is efflorescence, a white or yellow crystalline deposit that can form on the surface of concrete or masonry. This is typically caused by water seeping through the wall and bringing dissolved salts to the surface as the water evaporates.
Efflorescence is generally harmless but can be unsightly. It can be removed by scrubbing the wall with a stiff brush and water, or by using a commercial efflorescence cleaner. To prevent future issues, ensure proper drainage and waterproofing around the retaining wall during installation.