Request - Colorize special pages

[Ratithoglys]

Would it be possible to be able to colorize tabs hosting special pages.
So far no regexp I tried seems to work on "about:*" and "moz-extension:" pages

[Adaephon-GH]

You can match "moz-extension:" pages with the regexp [0-9a-f]{8}-([0-9a-f]{4}-){3}[0-9a-f]{12} as all extension pages seem to have the extension ID as "hostname".

As for "about:" pages: I found out by accident that leaving the "Host" field empty on a non-regexp setting will lead to the chosen color being applied to any "about:" page, including the new tab page. I am not yet sure, if there are any side effects to that.