Muting the colors of a color table

Hi-

We have various displays where we map data to RGB or RGBA.
One of the users asked if we could tone down the saturation
of a particular background topography image so that data
overlain on top stands out more.

Not knowing anything about color, I tried adding in a
ConstantMap of .5 to Saturation, but that had no effect.

I though of using transparency, but that is going to be
order dependent so isn't really a solution.

For a given color pallete, what's the best way to "mute"
or "tone down" the colors?

Thanks.

Don
*************************************************************
Don Murray                               UCAR Unidata Program
dmurray@xxxxxxxxxxxxxxxx                        P.O. Box 3000
(303) 497-8628                              Boulder, CO 80307
http://www.unidata.ucar.edu/staff/donm
        "Time makes everyone interesting, even YOU!"
*************************************************************