Yes they can have highlights. For example, someone with dark blond hair could have lighter highlights.
Sometimes blond hair (both natural and dyed) can have a greenish tinge, if for example the hair has a reaction to chemicals in a swimming pool.
My daughter has very blond hair and her hair turned greenish after swimming in a pool abroad. I doused her hair in tomato ketchup (yes, it does work!) then shampooed it and it was back to normal.
I know a woman with albinism who has platinum coloured hair and she dyes her hair a darker shade of blond.