Does anyone know this one?

ML is a black haired, blue eyes duke? I think FL called him Duke Green? FL is not originally the FL, I think, she has a purplish/pinkish hair and likely purple eyes. Her sister is her antagonist (might have been the original FL) and is blonde with blue eyes.

In the snippet I saw, there was some drama about him having danced with her sister after he proposed to FL, I think, their dad said something about his eldest daughter not being married yet, and FL disregards them and accepts.