Bottle blonde
Definition 1 of 1
Pro Tip 1/3Colloquial Usage
Used in casual conversation, not in formal writing or professional settings. 
At the reunion, I could tell she was a bottle blonde by her dark roots.
Pro Tip 2/3Possible Offense
May sound critical or offensive. Use cautiously to avoid implying judgment about someone's appearance. 
When he called her a bottle blonde, her smile faded.
Pro Tip 3/3Gender Neutral
Although more often used for women, it can refer to any gender dyeing their hair blonde. 
He showed his friends a throwback photo when he was a bottle blonde.