A subcommand of [Tk]'s [winfo] command.

'''winfo rgb''' ''window color''

Returns a list containing three decimal values, which are the red, green, and blue intensities that correspond to color in the window given by window. Color may be specified in any of the forms acceptable for a color option.

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Note that "winfo rgb" is ''not'' idempotent (or surjective) over the space of decimal triples.  [CL]
believes that the point is that the range space of "winfo rgb" is the display's color palette
(is that the right GUI vernacular?), and
is thus smaller than the full cartesian product ([[0-65535]],[[0-65535]],[[0-65535]]) one might
otherwise expect.

This presented with [VNC] service for which 
    winfo rgb . #ffff1fffffff
is 
    65535 0 65535
rather than the
    65535 7967 65535
delivered by a better-endowed display.

A start to a work-around for this is ...

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[Category Command] | [Tk syntax help] | [Arts and Crafts of Tcl-Tk Programming]