bug#4033: 23.1; list-colors-display is misleading

[Eli Zaretskii]

> From: "Drew Adams" <drew.adams@oracle.com>
> Cc: <4033@emacsbugs.donarmstrong.com>, "'Eli Zaretskii'" <eliz@gnu.org>
> Date: Tue, 4 Aug 2009 16:55:44 -0700
> 
> Emacs supports 16 bits per component internally, doesn't that mean that it
> supports up to #RRRRGGGGBBBB?

It supports that, but it cannot actually display that if the display
driver has only 8 bits per component.  I.e., the extra bits get lost
when the color is actually displayed.