Maybe I'm totally missing your point, but pink hair and good grades are not mutually exclusive, right?
Yes, when you're being graded on establishing rapport with patients, developing others trust in your judgment, maintaining professional working relationships across age, cultural, and socioeconomic divides, and being LOOKED to as a leader, pink hair and good grades are mutually exclusive. When you rise to a leadership position, you will begin to understand this.
Compared to the sacrifices we are all going to have to make throughout school, residency, and our professional practices in order to be successful physicians, hairstyles barely even register as an afterthought. You're going to subject yourself to seven to ten years of persistent judgment by others to prove that you have the commitment and sense of priorities required to be entrusted with potentially life-or-death decisions for your patients. If a little streak of pink or blue or whatever in your hair registers high enough on your priority list that you'll risk poor evaluations in order to keep it, then you really need to rethink your priorities.
If, as I suspect, you like unusual hair or clothing because it expresses your individuality, then you are probably sophisticated enough to know that you are not your hair or your clothes. Want to stand out in a crowd? Stand out by out working your peers and tackling tough problems. Don't do it by painting a target on your back.
I don't mean to sound as harsh and condemnatory as I do here, I'm just trying to express this flat out, and it's hard to express this in an even-sounding tone on a forum post. I'm sure you will make a fine doctor.
🙂 Just understand what your personal grooming choices express to those around you.