*motivational post snip*
More to topic: what color hair do you think Cullen has? It feels like it changes a lot between the games (probably because of the lighting). I can't decide if I think his hair is blond or sort of ginger/ strawberry blond. Maybe even light brown. 
I think it's dark blond. It does funny things when lighting changes. The hairs also look interesting under microscope (we totally compared all our hair under microscope back in the uni), it's transparent, and when you have thick hair, it looks darker. When it's dark - it looks darker. When it's dirty or wet - it looks darker. It also doesn't hold the pigment well under the sunlight, so I thought that's what made Cullen look more blond in DAII - he was spending more time outdoors, and sun bleached his hair a bit.
When greying such hair goes straight into white, I think, because, again, it doesn't hold the pigment well, and doesn't have a lot of it.
When people start greying - I think it's genetics and some other factors, like stress. I don't know about the former regarding Cullen, but he had a lot of the latter, so I wouldn't be surprised if he has white temples now, although the hair there will be transparent, and it won't be very obvious.