The designer probably used these colors because they thought it looked cool. Stop it. Make it because it’s right, because it has meaning, because it will help users solve a problem, or because it will help sell your product. Don’t do it just because it looks cool!
Considering how much better it is for followers to navigate content using the publication format, I’m a bit baffled that Medium don’t open this formatting option to regular accounts. It would solve the issue for brands and people who only post via a single log in, but still want the option of presenting their content in an easy to digest format. Of course, Medium may open things up in the future if there’s enough demand (if you do want this usability, highlight this paragraph, or comment and tag in @Medium so they know what’s up).