This is probably going to take some more iterations of ray tracing to sort out. Plus, when coupled with both hairworks and ambient occlusion being changed while the assets are presently loaded into RAM, it could be playing with how the ray tracing is viewing the light that needs to be scattered.
When using Hairworks, it treats each "lock of hair" as an individual 3D object. That, in turn, affects how shadows and AO work, which will inevitably darken the appearance of Geralt's hair. Add ray tracing to that, and you have even more possibility for shadows and such.
Also, when you switch that sort of graphical setting during play (whithout first closing the game and restarting it,) while it may work, it can also introduce weirdness. Remember that modern video games are a sort of "system of systems"; it's possible for one part of one system to inadvertently affect another part of another system in an unexpected way -- especially when trying to make adjustments in real-time.
(My recommendation here is to see if you can get these issues to occur without changing settings while playing.)
