[Users] Updating colors in message list by message status?

[Philipp K. Janert]

I'd like to have messages appear in different colors
in the message list - say, red for "new", blue for
"unread", and black for "read".

I thought this was easy to achieve by means of a mail
filter. However, the mail filter only applies when
the mail arrives, but NOT when it changes status later.
Specifically: when a mail is read, it does not change
color.

Is there a way to achieve the effect I am looking for?
(I looked, but I could not find a "hook" that would 
trigger a filter rule upon status changes or, more
generally, on user actions.)

Best,

		Ph.