In this photo I shot the columbine with a blue background (i.e., blue construction paper). While in PhotoShop I opened Luminar 4 and selected Artificial Intelligence Sky Replacement. Luminar 4 automatically figures out what is sky and what is not sky and masks out the flower. You can adjust the mask if needed. I used the default. I then used one of Luminar 4's many choices of sky. Here you can see the original and the new image with the sky.

For my photography club friends: I shot this using my Olympus OM-D E-M1 Mark II. I used a tripod and a 60mm macro lens as well as a cable release. I shot these at ISO 200, F9, 1/6 sec. I used a light box for light. I shot 8-15 photos varying the focus and did focus stacking in camera to get the flower in focus. Minimal post processing in LightRoom and PhotoShop.

Before Clouds

After Adding Clouds