The lighting, the scene, all are the same. But her hair looks bad in the second image. It's not the same as the first. The only thing I did different is change the pose and ran all the cloth and hair sims. The camera angle is a bit different, and I am not sure if I used the posing camera for the first image or not.

But what could cause such a drastic color difference in her hair?

If I had a nickle for ever time a woman told me to get lost, I could buy Manhattan.