I think the made some deliberate changes to each already established character in the effort to make everyone look unique. This isn't a bad thing at all in my opinion. Eye color changes, are a bit weird, and I'm not sure the rational behind that, but on a personal-superficial level, as a person with brown eyes, I get tired of all the heros/beautiful people having blue eyes. Everyone in DA2 looked like a wax supermodel, albeit Cullen was damn cute, I look forward to a more unique Cullen.
Hear, hear!
One of the things I love about Dragon Age is that the "good guys" aren't all blue-eyed blondes. By "good guys," I mean "sympathetic characters," since DA games generally give every character both virtues and vices (with a few unfortunate exceptions). Light hair does seem to be a little better represented than in the general population, especially red hair, but not implausibly so, and not surprisingly so, when you consider that the engine renders lighter pigmentation better.
At the moment, I'm head-canoning that stress and time are taking their toll on Cullen, and that the lightening of his hair is due to the presence of silver hair among the gold, but really, what I notice most is that he has hazel eyes. I look at close-ups of Dorian with his gorgeous, intensely colored irises, and I anticipate what Cullen's will look like. I'm pretty sure that they won't be exactly the same shade as Dorian's. The new engine seems to allow far greater customization in terms of available eye colors, and that's exciting. What if the character creator allows you to pick two eye colors (inner ring and outer ring, not heterochromy)! I get giddy thinking about honey-brown eyes with chocolate borders, or icy grey eyes ringed with slate.
And I'm looking forward to greater variation when it comes to hair color, too. I'm lucky enough to have a computer that can run the games, so I've enjoyed mods that improve the hair textures and available colors, but I'm eagerly anticipating the news that I won't have to install mods for that anymore. My favorite Hawke had deep auburn-tinged brown hair, pale skin, and darkest brown eyes. I'd like to see what the new engine can do with that combination.