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echo "Opus.editorBackground: white" >> ~/.Xdefaults
xrdb -load ~/.Xdefaults

You only need to do this once and cadence will have a white background every
time you run it after that.

I don't know how to change the colors of anything else.
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In the "Virtuoso Schematic Composer User Guide" Chapter 11 states that:
Changing the Background Color of a Schematic Window
To change the background color of the schematic window, do the following:
1. Open the .Xdefaults file in edit mode.

2. Change or add the option Opus.editorBackground from black to the color you
desire. For example:

Opus.editorBackground: green

3. At the UNIX prompt, type
xrdb -load ~/.Xdefaults

If you do not know where your .Xdefaults file is located, you can change the background
color of the schematic and layout windows by doing the following:
1. At the UNIX prompt, type
xrdb -query > xyz
This stores all the current system .Xdefaults variable settings in the file xyz.
2. In the xyz file, change or add the option Opus.editorBackground from black to the
color you desire. For example:
Opus.editorBackground: green
3. At the UNIX prompt, type
xrdb -load xyz
4. Restart your Cadence software.
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If the file .Xdefaults is not there, then create it using xrdb -query > .Xresources
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Inverting color scheme in schematic needs some procedures.
1. Quit Cadence Tool
2. Type the following command in the terminal

echo "Opus.editor.background: white" | xrdb -merge

3. Re-run Cadence Tool and open your schematic
4. Your schematic should have a white background now.

To save as an image, press ALT+PrintScrn.

If you want to get back to a black background,
1. Quit Cadence Tool
2. Type the following command in the terminal
echo "Opus.editor.background: black" | xrdb -merge
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REFERENCES
1. Cadence Design System, Inc.,Virtuoso® Schematic Editor User Guide, Product Version 5.1.4.1, Chapter 11, October 2008.
1. Cadence Design System, Inc.,Cadence Design Framework II Configuration Guide, Product Version 5.1.4.1, October 2008.