Minor Description
Since all other aspects of a Prompt's presentation can be set by assigning body content to a Prompt, it seems natural that the message text (inside a Label) should be able to be styled as well, in order to fit well with the other content.
The simplest way to do this would be to add several styles (as in "messageFont", "messageColor", etc.) to Prompt that would set the appropriate styles in the Prompt.messageLabel.