I did not read all the posts so this may be a repeat.... It's all about contrast. Red is a "dark" color and yellow is a "light" color. I usually like light colors on top and dark on the bottom. Now with that said I also like light on the bottom to off set the dark. Use large patches of light and dark. Most checker board merges to one color in the sky. There was a good article about this someplace. Maybe here on RCU or maybe another forum or even on the interweb???? Maybe Google will be your friend on this.
Ken