If you use the 256 AutoCAD colors to create color plots, you should be aware that your personal screen setting can affect your plots.

In color plotting, when your CTB or STB file is configured to Use object color, it plots the color assigned to the color number. However, the actual RGB color assigned to each color number is determined by a personal preference configuration.

AutoCAD uses two different color palettes, and the one it uses is based on your 2D model space background color setting. That means the same color drawing plotted by two different users with different background color settings will result in different color plots.
AutoCAD uses different color palettes for black (dark background palette) and nonblack (light background palette).

Important Note: My use of the terms light and dark have no connection to the Window Elements Light and Dark settings found on the Display tab of the Options command.

When your 2D model space background is set to Black (or near black), it uses the dark background palette. The setting threshold appears to be 30,30,30 as the darkest background to use the “light background” palette. One setting darker, a setting of 29,29,29, switches to the “dark background” palette. It is important to note that the default AutoCAD setting is 33,40,48, which is based upon the “light background” palette.

Note the RGB differences in Color 186:

Above: light background palette

Above: dark background palette

Again, these differences are based upon the 2D model space background setting — even when you are currently in a Layout tab (paper space) with a sheet/layout white background setting.

Be aware that National CAD Standard (NCS) version 5 defines its required RGB values for each color number in Section 3.0 Color Plotting. The NCS requirement matches AutoCAD’s dark background palette, which is not your installed default setting.

When using AutoCAD to generate color plots, it’s important to be aware of the impact your personal preference setting has on your plots.

Notes from Cadalyst tip reviewer R.K. McSwain: Good information regarding the current National CAD Standard and how the same color could potentially print differently under certain situations.