De-lighting was a delightful task.

The Unity-Technologies github is full of interesting bits of tech and branching endeavors. The "de-lighting" is one such tool that can be found within the organization's repositories and does exactly what it sounds like it would do; delightfully, de-lights 3D assets. De-lighting tools are useful while you are working in the 3D photogrammetry space and are looking to achieve a believable level of realism.

Certain amount of retopo is involved in any type of photogrammetry

Tool may only be usable in Unity 2017+

End result may not be exactly what you want (initially) but some correction and "parameterizing" should fix discolorization.