The answer to 'retaining wall installation yellowing' is that yellowing of a new retaining wall is a common issue caused by mineral deposits or efflorescence. This happens when salts and minerals in the concrete or mortar leach out to the surface, leaving a white or yellow discoloration.
Efflorescence is not a structural problem and is usually just an aesthetic issue. It can be removed by scrubbing the wall with a stiff brush and mild detergent or vinegar solution. Preventing efflorescence long-term may require adjusting the wall's drainage or using a sealant. If the yellowing persists or worsens, it's best to consult a professional landscaper or masonry expert to diagnose and address the underlying cause.