Most Helpful Girl
I wouldn't worry too much about it. She's not going to keep it pink forever. And I think what your friend suggested you say to her is good, but just don't outright say to her that you hate the pink.
Most Helpful Guy
You really can't say anything here. She's your girlfriend, she is ALWAYS beautiful, period. If you aren't willing to end the relationship, just get over it. Nothing you say will go well here... you are her biggest fan, right? If you cannot live with the fact that she has dyed her hair an awful color, your relationship probably isn't going to last very long anyway. I don't want to sound negative but, take her or leave her.