"On the side of your render pane is a little expansion box. Open that, and if your dome is visible, you can adjust tone mapping during a render without losing progress of your render. You can even do it once the render is complete. Then you will know if ti is the tone mapping or not."

Render settings? I see tone mapping in there - adjusted some of the settings for test renders. Still the hair looks white instead of blonde.

I can't change those settings during a render.