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