I was recently asked whether I preferred Howl (from Howl's Moving Castle) with blonde hair or black hair.
I answered blonde, because in the movie he looked super pretty with blonde hair and I love me some pretty boys, and because in the book he kept his hair blonde and had this to say when Sophie states that at least her hair color's natural: "I've never seen why people put such value on things being natural."
But then, as I am wont to do when I start to get sleepy, I started thinking about it a lot harder than was really necessary. After a few minutes of musing, I came up with the theory you're about to see. I'm posting it here because it didn't seem like the sort of thing to put in my gallery, as it's just me rambling.
Anyway, I hope you enjoy, and comment with your thoughts on the subject. Or perhaps comment on how pitifully bad my need of a life is...
I think Howl keeping his hair blonde in the book symbolizes how you don't (and shouldn't) have to become someone totally different to find someone you love who can love you back, they'll change you, of course, but they should fall in love with who you are, not who they want to make you.
On the other hand, Howl allowing his hair to stay black in the movie might symbolize how his love for Sophie has helped him shed the facade he had built up around himself to keep safe from the world, allowing him to finally be who he was on the inside.
So, when you look at it like that, either one is fine. Really, liking the black/blonde haired Howl is more about their different relationships than their appearance and how they each overcame their problems to finally get their happy ending.
(only probably not, since I doubt anyone else has thought much past which one looks nicer and I'm just being weird again)