Black colour absorb heat from sun ray . White deflect part of the sun ray and stay cooler. But here something , vent cover are not really white but kind of translucent letting heat ray get inside . Black block this.
For AC , I do not believe this will make any difference . And yes, black is better at UV IF they put enough carbon black and I have strong suspicion they don't . Also with black plastic part , you can use more recycle products and the customer will not know.
PS I work in the plastic raw material all my life.