The answer to 'retaining wall installation yellowing' is that the yellowing of a newly installed retaining wall is often caused by efflorescence, a natural process where salts and minerals in the wall materials come to the surface and leave a white or yellow discoloration. This is a common issue with concrete, stone, and masonry retaining walls and is not a structural problem.
The main causes of efflorescence are excess moisture, improper curing, and high salt or mineral content in the wall materials. It typically appears within the first year after installation as the wall dries out. While unsightly, efflorescence is not harmful and will usually fade over time as the wall fully cures. In some cases, it can be removed with a mild acid solution or power washing, but DIY removal is not recommended as it can damage the wall.