Most of the time when you highlight the hair, there are chances that it will look brassy. The brassy look can be seen on your hair even if your visit a hairstylist for the highlighting process. This is a very common problem if you have hair color with brown and also orange undertones. So to make the highlighted hair look less brassy, you have different options to follow.
The first and most important option is washing your hair with purple-based or blue-based enhancing shampoo. Then apply a proper hair conditioner over your hair to make the highlighted hair less brassy. Once the conditioner is left in your hair for more than minutes, try to rinse it normally. The next way is using blue-based toner on your hair with level 9-10 option. To do this you must take 10 volume peroxide developer and mix it with the selected toner. Then spread the mixture over your hair and leave it for around ten minutes. Then rinse the hair using warm water to keep the brassy look out of your hair. Whenever you are planning to wash your hair, try to use the water that has no iron deposits as it is one of the most important reasons for the brassy look in your hair. Also cover the highlighted hair while going out of your home with hat to keep the sunlight away from it as your hair can turn brassy due to UV rays produced from the sun.