Along with the [color values available for syntactic use in Tcl scripts], several other facts about color might interest programmers. This page aims to collect all this sort of information.

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Okay, here's the standard (and rather reliably portable) 6x6x6 color cube.  This page has been
around forever:
   
   http://the-light.com/colclick.html

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The source file which realizes the description which appears in the hyperlink at the top of this page is xlib/xcolor.c.  X11 (Unix) systems often have a `showrgb` command and/or .../lib/X11/rgb.txt which give the same (?) data.  Programmatic access to the English-to-RGB-code map is available as

  winfo rgb . $color

[RS] has this wrapper to format the returned list of three decimals to the #RRRRGGGGBBBB form (all in hex) used in color input:
 proc colorhash color {eval format #%04X%04X%04X [winfo rgb . $color]}
 % colorhash red
 #FFFF00000000
 % colorhash green
 #0000FFFF0000
 % colorhash blue
 #00000000FFFF
 % colorhash white
 #FFFFFFFFFFFF
 % colorhash black
 #000000000000
 % colorhash grey50
 #7F7F7F7F7F7F

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"[Color pickers]" answers common questions on this subject.

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The [W3C] maintains a list [http://www.w3.org/MarkUp/Guide/Style#colors] of "Web-safe" colors.

[KPV] - here's that list, along with the closest named Tk color:

   W3C NAME    RGB        Closest TK color (~ means not an exact match)
    black     #000000   =>   black
    silver    #C0C0C0   =>   ~gray75 (or SystemButtonFace on classic Windows)
    gray      #808080   =>   ~gray50
    white     #FFFFFF   =>   white
    maroon    #800000   =>   ~darkred
    red       #FF0000   =>   red
    purple    #800080   =>   ~DarkMagenta
    fuchsia   #FF00FF   =>   magenta
    green     #008000   =>   ~green4
    lime      #00FF00   =>   green
    olive     #808000   =>   ~Gold4
    yellow    #FFFF00   =>   yellow
    navy      #000080   =>   navy
    blue      #0000FF   =>   blue
    teal      #008080   =>   ~turquoise4
    aqua      #00FFFF   =>   cyan

NB. what TK calls green is actually lime for W3C

''[MGS]'' 2003/03/21 - These are not the "web-safe" colors - they are the 16 colors defined in HTML 3.2 and 4.01 and correspond to the basic VGA set on PCs. The "browser-safe" colors are constructed from colors where red, green and blue are restricted to the values:

   RGB  00  51 102 153 204 255
   HEX  00  33  66  99  CC  FF

... which gives 6 * 6 * 6 = 216 different colors.

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[xcolors] is an interesting command under X11.

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International Color Consortium maintains a page [http://www.color.org] which has information on ICC color profiles for computer color matching.

Mildly related to this is "[Selecting visually different RGB colors]".

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'''Percent to color''': The following routine produces a color from an integer between 0 and 100, where 0 is red, 50 is yellow, and 100 is green (useful e.g. for painting progress bars):
 proc percent2rgb {n} {
    # map 0..100 to a red-yellow-green sequence
    set n     [expr {$n < 0? 0: $n > 100? 100: $n}]
    set red   [expr {$n > 75? 60 - ($n * 15 / 25) : 15}]
    set green [expr {$n < 50? $n * 15 / 50 : 15}]
    format    "#%01x%01x0" $red $green
 } ;# RS

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"Color manipulation" [http://aspn.activestate.com/ASPN/Cookbook/Tcl/Recipe/133529] is the name of an ASPN recipe.

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'''Random color:''' [EE] presented this simple beauty in the [Tcl chatroom] on 2002-12-18:

 proc randomColor {} {format #%06x [expr {int(rand() * 0xFFFFFF)}]}

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[Tk syntax help] - [Arts and crafts of Tcl-Tk programming]


[[Discuss
Death of the Websafe Color Palette?
        URL:
          http://hotwired.lycos.com/webmonkey/00/37/index2a.html?tw=design
later.]]

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[Harmonic color wheel]