In iMovie you can force a video clip to more closely resemble another clip by using the Match Color tool. This simply adjusts the color of the first clip to match the colors in the second. You can use this to prevent jarring transitions between very different clips, or to match similar scenes that were shot using different light. You can also use Match Color with images or between video clips and images.
Want to know more about how to use iMovie on your Mac? Check out this MacMost course!