I receive this question regularly in my chair, "Should I come in with clean or dirty hair?".
If you're coming in for just a haircut, dirty is just fine. We're going to wash it before getting started anyway. If you're coming in for a Color or Lightening service, I personally don't mind either way. Professional color products have come so far and can really work some magic. With that being said, if you know you have stubborn hair, you may want to wash it at least the day before, and not have any dry shampoo or lots of other products in your hair when you come in. This will help the colors do what they're made for without having to cut through all of the products and dirt in your hair first, resulting in better results overall. Imagine painting on a canvas covered in dust and other junk. You could get the job done, but it may not be as good as it would have been if the canvas was totally clean.
Let me break this down a little more...
Again, if you are going to see your stylist for a haircut, it’s not necessary to wash your hair. The only case that could justify washing your hair is if it’s loaded with dry shampoo or texture spray and it will be too challenging to brush out. In that case, it would be really helpful for you to go ahead wash it beforehand.
If you are going to see your stylist for color (including lightening services), it’s better to arrive with clean, dry hair. The reason behind this is that it preps the hair to fully absorb whatever color service you are having done without the barrier of dry shampoo, texture powder, oil, sweat, etc. If your hair is covered in hair product, how do you expect the hair color to respond? Another great reason to have clean hair is to ensure a perfect color match. Hair tends to look darker when dirty. In most cases, it’ll all work out fine, but arriving at your appointment with clean dry hair gives the color the greatest opportunity for success.
So, if you’re able to wash your hair prior to getting it colored, even the night before, it’ll certainly help set your stylist and the color up for success. If you aren’t able, it's not a deal breaker at all. Your stylist may just need to take some extra steps before getting started with color application, but all should still be fine.