Level 6 hair is light brown! For the best possible color, you'll still want to stick with SUPER pigmented/bold shades! When your hair is healthy (unbleached) it's going to be less porous and therefore it may not hold color as long. Colors that last 6 weeks may only last a week or so on healthy brown hair! If your hair is darker brown these colors should still give you a nice tint but keep in mind that each color has a hair level chart so that you can get an idea of how it will look on your hair!
If not wanting to bleach your hair, you should wash your hair with a clarifying shampoo (like our Prepare to Dye Clarifying Shampoo) but do not condition it at all. This will remove dirt and oils in the hair while also opening the cuticle. Results vary from person to person because everyone's hair is different, so regardless if you decide to bleach or not, we always recommend doing a strand test to see how the shade will show up on your hair.
For most vivid results you'll want to pre-lighten your hair to around a level 7 blonde. Have questions? Reach out to our customer service team at firstname.lastname@example.org