My sister is working on a book. She asked my advice for creating a cover, since she has no money. I threw out a few ideas, with different colors and fonts, but she rejected a lot of them. Then, in true sisterly fashion, she went to the Internet and found that my color choices for her project weren't used in best sellers.
I had to find out more, so I searched the Internet, as well. Wow. My covers need redoing! Even the latest one probably doesn't pass muster for being in the best seller list.
First, stick to metallic and warm colors-gold, silver, or copper, or ochre (it's like a tan color). But what I'm seeing from the article (see The Bestselling Colors in the Book World), is that there's a color palette. They use three colors that kind of match, then a contrasting color.
This article (https://www.coverdesignstudio.com/best-colors-book-covers/) discusses using color to convey the mood of the book, as well as using contrasting colors to make things pop. Interesting and brilliant!
I also found these articles, talking about simple design, simple fonts, and books that look good as a thumbnail. Wow. Times have changed since I first got into this business. And, to tell the truth, I LIKE it!
14 Tips to Make a Best-Selling Book Cover
Yes, We Really Do Judge Books By Their Covers
Top 8 Cover Design Tips for Self-Publishers
Have a great week!