This image is a case where I saw the background first and then looked for a subject. I found a bank of purple flowers (Dame’s Rocket) I knew I had the color material for an interesting, saturated background. The subject I had in this location was a modest one, yellow mustard flowers:
After I took this I saw a color wheel, and realized that yellow and purple are on opposing sides – these are complementary colors or pretty close to opposites, the kind of color contrast graphic designers use to create visual interest. Those flowers would look nice on a green monochrome background, but the yellow/purple contrast has more impact. It makes a nice but forgettable flower look more interesting. Too bad yellow lady slippers weren’t growing in front of the Dame’s rocket!
Here’s another image, Helianthus, that I took a while back with a similar color scheme.