Lawless Lawyer - Not a biker but his uncle is the head of his mob and he sorta creates his own smaller group. He is a lawyer working for justice using gang like ways (without really crossing the line) to aid his cause. Lee Joon Gi (the actor playing the ML) is good looking and his character is really smart and can fight. There is a good romance (without being so heavy it gets in the way of the story) between Lee Joon Gi (who also acts in Flower of Evil) and Seo Yea Ji (from It's Okay to Not be Okay). Sorry, no coloured hair, bikes or earrings; not a bad car though.
For something completely different, the ML taught himself to ride a bike, is a gang of one (sorta hooks up with/becoms leader of another, I think) and goes up against another biker group. The actor isn't half bad looking, might have streaks in his hair, no piercings and definitely a romance. This one just entered my head when you mentioned biker gang so I thought I'd put it out there. Have you seen Greece 2?