My situation might have been a fluke, but when I applied for my passport I had dyed my hair brown (didn't even think about it). My hair is naturally blonde and I eventually dyed it back to blonde.
I applied in March, went to Europe in June. The security agent at the airport in Amsterdam called over his supervisor and made me stand against some wall while they all held up my passport, comparing it to me. They eventually made me put my hair in a ponytail and they decided I really was me.
It was a little freaky... I was so afraid they wouldn't let me board!!