Are the extensions real hair? If they’re not or if they’re coated with anything synthetic, the color wont take. If they are real, natural hair, it can be done. You will need to use bleach to lift them to match your hair. I recommend covering them with plastic wrap or foil to keep the heat in, and keep them in a warm or bright place so the color will take. This will take longer to lift than it would take to lift your hair (since its not on a person) so just keep checking on it and rinse it when it’s at the level you want it. It could take hours, but it can be done.