Allow setting the background color

[dkk]

The background color get's overwritten with white.

New Issue Checklist

• [x] I updated Animoji to the latest version.
• [x] I read the Contribution Guidelines.
• [x] I read the documentation.
• [x] I searched for existing GitHub issues.

Issue Description

I would like to set a different background (not white). But it does not seem possible without changing the code in the pod.

Environment

• iOS Version: 14.0
• Device(s): iPhone 11 Pro