On 2016-11-24 Thu 15:22 GMT-0800, Hong Xu <hong@topbug.net> wrote:

> Currently in message-mode all cited texts are highlighted in the same
> way. It would be nicer if the highlighting of different citation levels
> can be easily customized.
>

Here is a patch and a screenshot. The default colors I chose may not be
optimal -- but I guess I'll leave that part to professionals.

Add support for different faces for different citation levels in message-mode.

	* message.el (message-font-lock-keywords)
	(message-font-lock-make-cited-text-matcher): Add support for
	different faces for different citation levels.  The faces are
	defined in the faces named `message-cited-text-N': N of the
	Mth citation level will be M mod 4.
	(message-cited-text-1, message-cited-text-2)
	(message-cited-text-3, message-cited-text-4): Add customization
	for the faces of 4 different citation level.  In the future, the
	number of faces may increase, as the code is flexible enough to
	automatically deal with that.
	(message-cite-level-function): Add a function to customize the
	determination of cite levels given the prefix of the cited text.