but when I expand it to ANSI C or larger and print it on an HPDesignJet 5000 PS I get UGLY colors and lose detail?
Themarko,
Are you letting the plotter driver do the resizing? Are you enlarging the map, or printing it the same size just on a larger size sheet? If so and you dont have enough pixels in your image, resampling will take place which leads to lower print image quality and should be expected.
Two ways around this:
1. In arcmap change your layout size to the desired image size and assuming your shading is of an appropriate resolution for the scale of your map it should look better.
2. If generating a TIFF file to be printed with Illustrator or Photoshop make sure it is being generated at the appropriate resolution and size for your page. You can photoshop like crazy but just because it looks sharp on screen at 72 dpi does not mean it will print out well when enlarged to ANSI C at 144 + dpi.