Add and edit backgrounds in iMovie on iPhone
You can add a color background to your movie project. iMovie includes a number of solid, gradient, and pattern backgrounds that you can customize.
Add a background
Change the color of a solid background
Change the colors of a gradient or pattern background
In the iMovie app on your iPhone, open a movie project.
In the timeline, tap the background clip you want to customize.
In the top-right corner of the viewer, tap the Color button .
Two Color buttons appear in the viewer, showing the primary and secondary colors used to generate the gradient or pattern.
Do any of the following:
Set the primary background color: Tap the first Color button (on the left), then choose a color from the available options.
Set the secondary background color: Tap the second Color button (on the right), then choose a color from the available options.