Dear aspirant

Hair color although doesn't cause much problem in appearing for exam. If they are only light shades of red colour blend with your natural hair color then I think it's not much problematic.

If you have changed your whole hair colour then it will affect your appearance from the photo which you uploaded during application form or photo on admit card. So if the examiner had no objection about that they are quite convinced you are same person as on admit card then there will be no problem otherwise this may lead to little issue during entrance and you will have to fully convinced them that you are the same person.

So it's better to be in your natural appearance as yours uploaded photos in the application form.  If you done little blend and mixing then it will be not problem.

Hope you have got your answer

All the best