color bar when printed in black and white

[Dazhong Yin]

Hi folks,

I would like to generate a color bar using cbar.gs for shaded plots that if
I print these plots in black and white, the color bar would gradually
increase darkness from bars for small values to bars for big values, or vise
versa. I am no artist and do not know how to mix rgb to get this effect. Has
anybody tried this?

Thanks for help!

Dazhong