Hair color keeps changing

This is probably an issue with how the reflections and shadowing of 'Stranded Hair' is handled in the engine. When direct lighting and light reflections from the game environment hits the hair, each strand of hair begins to reflect the light onto every other strand. Since a reflection is, in effect, considered a light source of it's own, it starts a chain reaction where every strand has to respond by casting shadows onto every other strand, virtually simultaneously. 

Light colored hair is more chromatic and reflects more light, but since the hair strands are so close together, the amount of shadows being created tend to overpower the reflection, making the hair appear darker than it should. Even in direct contact with very strong light sources like the sun, you will likely see a darker shade than what you expected. Lower light conditions, like entering the shade in an otherwise sunny scene, will still trigger the reflections and because of the extra chromatic nature of light hair, subsequently also start the chain reaction of casting a lot of shadows, making the hair appear very dark brown/grey or even black since the light source is less bright and won't cast as strong a reflection to combat the shadows as direct sunlight would. Darker hair colors tend to experience less of this effect since they are less chromatic and don't reflect light as easily, as well as not being so obvious in contrast when it does happen.