All I can say is the current behavior is quite annoying when more than 8 colors are available. Many colors have very low contrast against the grey90 background, and there's no way I can see to set the background to brightwhite. This forces me to set my TERM so that all I get is black and white, which can also be hard on the eyes.
> From: "Drew Adams" <drew.adams@oracle.com>
> Cc: <7943@debbugs.gnu.org>
> Date: Sat, 12 Mar 2011 12:18:54 -0800
>For compatibility with 8-color text terminals that cannot produce the
> > ("white" 7 (229 229 229)) ; gray90
> > ("brightwhite" 15 (255 255 255))) ; white
> >
> > As you see, what is called "white" in list-colors-display is actually
> > gray90.... This definition is used to leave FFFFFF for brightwhite
>
> Wow. I won't presume to suggest that this is misguided, but I can't help but
> wonder why. Why wouldn't white be called "white" and gray90 be called "gray90"
> or "off-white" or some such?
bright colors, IIRC.
Some text terminals can produce bright white by combining white with
another text attribute (bold, if I'm not mistaken). Having 8-color
terminals without "white" would be confusing.
We do use "gray" on terminals that don't have this historical
precedent, see w32console.el, for example.