Clean or Oily Hair & Highlights

Oily hair
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Q: I have highlights in my hair, but my roots are showing and I need them done again. I was wondering if it is better if I have clean hair before I go to the hair dresser.
Should I use conditioner when washing before highlights? My mom told me that you should have oily hair before you get highlights. Is this true?

A: For giving a color service, your stylist will want you to have "clean, dry hair". That means that you should shampoo and condition your hair, as you normally would, at least the day before your appointment.
You don't have to shampoo and condition your hair the day of the service, unless you use a lot of hair product. In that case, do go ahead and shampoo and condition the hair before your appointment.
Your mom's idea of having "oily hair" for a highlighting service has some merit, but isn't necessarily true. You want the hair to be in its best condition possible, which means you should have it well-conditioned, but only because having the hair properly conditioned ensures even penetration of the bleach and hair color.
Having oily hair is different from well-conditioned. Having the hair be "oily" could inhibit the ability of the bleach to penetrate the hair shaft and result in uneven color.
So, the night before your hair appointment, shampoo and condition your hair and dry it as desired. The next morning, style the hair with no product (or at least as little product as you can manage to use) and go to your appointment.
Keep in mind that hair products such as gels, hairsprays, waxes and spray laminators tend to coat the surface of the hair shaft and will block the absorption of the bleach by the hair, preventing the lightening you are trying to achieve.
See also:
How clean hair affects a hair coloring job