The suggested way to purchase solid colored extensions for highlighted hair, would be to match your “underneath” shade. You should basically have two shades in your hair, if it is highlighted. Depending on how many highlights you have, you may choose to match one color or the other.
How do you match ombre extensions?
When purchasing ombre extensions simply match the base color of the extensions to your own hair color and then choose the ombre color you want. Keep in mind, a more natural fade will look most natural, for example the chestnut brown ombre is the most popular as it looks natural and blends well.