If you are printing to a system printer, you can choose either dithered or nondithered output. With dithered output, the printer attempts to simulate more colors than it actually supports by mixing colors and white space to create the effect of a new color.
By default, AutoCAD LT uses dithered output for raster printers that support them. You can turn off dithered output on the Printer tab of the Preferences dialog box.
The Windows printer driver has its own control over dithering. Depending on the printer driver, you can set the resolution or pattern of the dithering.
Consult the documentation provided by the printer driver vendor for details about the printer drivers capabilities.