what is "primary" refer to in visual

[Zhang, Xing Z]

Thank you Simon and Mikhail. I understood.

> -----Original Message-----
> From: Simon Thum [mailto:simon.thum at gmx.de]
> Sent: Wednesday, March 17, 2010 12:07 AM
> To: Zhang, Xing Z
> Cc: xorg at lists.freedesktop.org
> Subject: Re: what is "primary" refer to in visual
> 
> Am 16.03.2010 09:42, schrieb Zhang, Xing Z:
> > Hi experts:
> >          From xlib manual, here are sentences for color:
> >
> > GrayScale is treated the same way as PseudoColor except that the *primary*
> that drives the
> > screen is undefined. Thus, the client should always store the same value for
> red, green, and
> > blue in the colormaps.
> >
> > TrueColor is treated the same way as DirectColor except that the colormap
> has predefined,
> > read-only RGB values. These RGB values are server dependent but provide
> linear or
> > near-linear ramps in each *primary*.
> >
> >        I apologize for my bad English, I am confused by the word "primary".
> I wonder what does
> > "primary" mean here? Thank you.
> 
> You may find this link helpful:
> http://en.wikipedia.org/wiki/Primary_colour
> 
> Cheers,
> 
> Simon