How do advertisers use contrast to make sure that their ads are noticed? Would the lack of contrast between the advertisement and the medium in which it appears help or hinder the effectiveness of the ad? What are the ethical considerations in employing such strategies?

How do advertisers use contrast to make sure that their ads are noticed? Would the lack of contrast between the advertisement and the medium in which it appears help or hinder the effectiveness of the ad? What are the ethical considerations in employing such strategies?