Remove `color` parameter in Broadcast Message API documentation

Problem to solve

• What product or feature(s) affected?
  • Broadcast Messages API. Specifically, the feature that allowed change of color and font parameters via API.
• What docs or doc section affected? Include links or paths.
  • The Create/Update a Broadcast Message API documentation.

• This Issue describes that color and font are not in use currently.

• Is there a problem with a specific document, or a feature/process that's not addressed sufficiently in docs?
  • The broadcast message feature had color parameter change to theme. This is not updated on the API documentation.
• Any other ideas or requests?

Further details

Issue raised by Self-Managed Premium customer, requesting custom way to change color through the API: #294651 [Internal only]

Proposal

Remove color from the Broadcast Message API Documentation section for the sample request.

Who can address the issue

Other links/references