See
http://purl.org/tcl/home/man/tcl8.4/TkCmd/colors.htm
and [Tk_GetColor].













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Examples:
    #FF8080
    #F80

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Jeff Hobbs color_demo (http://tcl.ActiveState.com/community/hobbs/tcl/capp/) is a great little application for picking colors (via their names, not values).