Color Matching Plotter

I use Autocad 2005 and HP500 with HPGL/2 card. I am trying to plot color plots from autocad but the color of the objects (lines, hatches etc) are not the same on plotter as on screen. I have that problem with autocad 256 standard color pallete and with color books and true color as well.
I optimised my HP500 printhead by using the automated procedure on plotter to make sure that plotter can represent exaclty what is sent by the application.
When I plot a color raster image from inside autocad everything plots almost perfect. BUT vector lines that have the same color as portions of the image actually print differently. I think that it is an autocad problem or a parameter.
Many other colleagues have the same problem with Autocad 2005 and the HP500. I am using the HP driver supplied with Autocad 2005 Installation CD (driver version 5.35).

I also plotted the Autocad color wheel and the result is much different than the screen.
I tried to plot the color wheel on my Canon i560 A4 printer and I got the same results.

How can we make the neccessary adjustments in Autocad to plot correclty colors
Yellow plots a bit greenish and
Light red always plots dark.

Stelios Patsoumas
Architect NTUA