Is it wrong for a guy to tell his girlfriend, he doesnt want her hair to be dyed blonde ?

Yes, it is her decision.

Why is that wrong for him to voice his opinion if it's his preference?

Ultimately the decision is hers in the end

If she has long hair it can be any color.

depends what the reason is that you don't want her to dye her hair, but end of the day it's her hair, her choice

not wrong, but it may not go well.
be sure to empasize that you you'll love her no matter how she looks and that ulitmately the choice is hers. And have a list sincere reasons ready about what you like her hair the color it is now.

And maybe ask yourself if it really matters in the long run. She's looking for a change. Hair color is an easy way to achieve that. Being single is another way.

Not in my opinion. I'd make the same request. Only in begging mode. Could mean the end of the relationship. Just me, tho.

Depends on the woman. Most live the old fashion life (like me) that listens to what he says and then you have the newer generations where both wants to wear the pants in the house

I think its ok for him to voice his opinion, it would be the same if that same guy wanted a green mohawk.. i would think that female can and would voice her opinion..right?

I think creativity is the fun of hair. You can color and cut it however you want (ok, you can over do it), but it's just temporary. Eventually it just goes back to how it started.

No, he has the right to tell her that he prefers that she not dye her hair blonde…..however, she also has the right to dye her hair any color she wants.

No it's not, but he should respect her decision nonetheless

Good luck...you'll just make her want to do it mkre

Share your opinions. Her choice how she keeps her hair.

He can tell her, but it's her hair, so her decision.