Can I use a color other than the color of a bundled cable on a command computer?

Everytime I try the computer just shuts down.

Advanced and Command Computers run multishell. Multishell runs all terminal calls through windows. Windows error out if you attempt to use anything other than the sixteen colours to draw through them, and may indeed take the whole system down with them when they do.

So… don't do that. Set valid colours instead.

No, not possible now. 16 colors are hardcoded into computercraft.