Well said @Massmomm. If a school is not going to accept a prospective student due to their hair color, a piercing or a tattoo, then the student likely would not want to attend that institution. It’s 2016 for crying out loud. Even for an interview, if a student tends to wear their hair in a certain color, has a tattoo or a piercing, what does it matter? Dress neatly and cleanly, but why would we want somebody to not be who they are? A kid with dyed hair, a piercing and a tattoo likely will self select not to visit or entertain schools where everybody dresses in suits and sun dresses (an extreme example made for a reason).
Even this may be overlooked depending on the college’s campus culture and particularly the interviewer.
For instance, some alum interviewers at my alma mater, particularly those who resided in a certain neo-hippie dorm notorious for its residents’ lack of personal hygiene when I attended wouldn’t have minded. If anything, those in the latter camp may actually regard it as a plus.
Granted, this is an anomalous case and you’re usually better off assuming dirty clothes are a no no. 
If it’s who she is… I wouldn’t worry about it at all. Hard science or not. In fact, I think I’d encourage no change at all. Why present yourself as someone you’re not? You’d wind up picking a school that’s not a fit. IMO
Went to my D’s college band concert last week, and saw at least 8 different bright hair colors represented.
The tour guide we had at Bryn Mawr had purple hair. She was a great tour guide and we liked her a lot. I say don’t sweat it.
Agree for tours and info. sessions it is a non-issue. If she still has dyed hair when she does one-on-one interviews she would need to consider how she wants to present herself – but if her appearance is neat and clean I don’t think it would be an issue there either.
Daughter should absolutely be herself. I too have one with the color thing going and wouldn’t consider changing it for a tour at any school. With many kids, I have probably done 30+ tours, seriously. What stands out to me on every tour is the obvious “first time tour” parents, typically overdressed and trying to impress, with horrible shoe option for all the walking. I was one of those, just the first time, then realized it is all about being comfortable, and most times no one knows or cares who you (parent) are, although the kids have a chance to introduce themselves sometimes. The others that stand out are those overtly trying to convey they have enough to pay full boat at the privates (way too much jewelry for a walk around campus 
). Sometimes it is brutally hot and these things are long…and no matter how good you look when you start, you can be a bundle of sweat when it is over. It is really a fun time to people watch - enjoy them, but be yourselves and dress comfortable and it is more likely to be a fun/pleasant experience. Oh one last thing, I suggest carrying a bottle of water…drinking fountains seem to be a thing of the past on a lot of campuses, and almost a couple hours of hills and stairs can bring on the thirst!
Interviews, agree, still wouldn’t change hair, but would give some thought to the overall appearance. Good luck!
Okay, I admit that I am strict, but I didn’t let my older daughter dye her hair in HS. . .until she got into Harvard and asked to dye her hair Crimson. I said go for it. What else could I say?
I think colleges are pretty use to hair dye and piercing at this point.
Echoing others- would someone with violet hair really want to go somewhere that they’d negatively judge her for it?
Personally, I’m a PhD student with dyed, very bright red hair. Lots of the students I see walking around campus for tour visits have hair all different colors of the rainbow. I think it’s awesome
Echoing romani, I’ve seen several PhD students and Profs…some well into middle/senior years who sport non-natural bright dyed hair at academic conferences.
Even in fields known for being relatively stodgy in many areas like poli-sci though it seems far less common there than in less stodgy fields like history or moreso sociology.
I wonder if the same people who sport “unnatural” colors are the ones who get all revved up about living naturally and organic and “toxins”?
"The others that stand out are those overtly trying to convey they have enough to pay full boat at the privates (way too much jewelry for a walk around campus ). "
Or it just means their everyday jewelry is nice, that’s all. Jewelry doesn’t prevent you from walking about, the way that inappropriate shoes might. Sorry, like it or not, there are affluent women who have nice jewelry and wear it everyday. Why should they not? The “trying to convey they are full boat” seems like pure projection on your part.
For what it’s worth, I recently put unnatural colors in my hair and I didn’t lose my job!
Of course some women have and wear nice jewelry and aren’t trying to convey anything.
And some people dye their hair and it has nothing to do with their views on organic food or toxins.
FWIW, Manic Panic dye is vegan 
What on earth does a hair color have to do with toxins and living naturally or whatever?
I have little tolerance for people worried about pseudoscience and I am a vegetarian but I have been for a very, very long time and have no interest in “organic” anything.
I just happen to like bright hair colors.
One other practical note on this: at some colleges, “expressed interest” matters in the admissions process. So at some schools, it will matter that you sign in for the tour/info session. That can help you. Asking stupid questions at the session won’t hurt you, though.
My DD’s lifetime best friend has always had neon hair colors and sports a ‘rocker’ fashion syle. My DD is actually probably the more ‘artsy’ of the two, but has a very ‘traditional’ look compared to most of her friends. Whenever my DD spots kids on campus with brightly colored hair, piercing, etc, she always comments positively, inferring that it’s a place where kids can be comfortable being themselves and have it understood that who you are is more than what is seen on first glance. She’s even moved schools up and down her list based on this (go figure).
We also depend on the “if this is a deal-breaker, then this school is probably just not the fit for you” line when she has incorporated a little respectful creativity or humor into essays etc.
I have a mid-thirties colleague who’s also sporting the purple look, has for years, so yeah, she’ll look like some of the professors, too.
I also have a couple students doing the dyed-gray “granny” look, which is sort of endearing, in a puzzling kind of way.
Part of me wants to go seapunk, though I expect I really won’t ever.
And who wouldn’t want to look like “Starry Night”?
Today I saw woman who was probably in her 70’s with pink highlights in her coiffed blonde hair. She wasn’t at all artsy looking, her clothes and accessories were totally suburban grandmother. I think we can safely assume wildly colored hair has gone mainstream.
I also agree that, even if this is a phase and your daughter is back to her natural color by time she starts college, she’ll probably be happier in a place that doesn’t look askance at purple hair.