Mastering Perl/Tk says that $widget->rgb(“colour”) gives values from 0 to 255 for the red, green and blue components of the colour.
As the attached Perl shows it seems to give a value approximately the square on these numbers.
I find I can get the range with the expression int(sqrt(red/green/blue)).
The output from the Perl is

colour <black> red <0> green <0> blue <0>
sqrt colour <black> red <0> green <0> blue <0>

colour <white> red <65535> green <65535> blue <65535>
sqrt colour <white> red <255> green <255> blue <255>

colour <red> red <65535> green <0> blue <0>
sqrt colour <red> red <255> green <0> blue <0>

colour <green> red <0> green <65535> blue <0>
sqrt colour <green> red <0> green <255> blue <0>

colour <blue> red <0> green <0> blue <65535>
sqrt colour <blue> red <0> green <0> blue <255>

Can anyone explain why is happening and/or is using the int/sqrt function is the correct thing to do to get the quoted range?

use Tk;
use strict "vars";

my (@colours, $col_item, $red, $green, $blue, $mw);

$mw = MainWindow->new;

@colours = qw(black white red green blue);

foreach $col_item (@colours) {

($red, $green, $blue) = $mw->rgb($col_item);

print "\n     colour <$col_item> red <$red> green <$green> blue <$blue
+>\n";

$red = int(sqrt($red));
$green =int(sqrt($green));
$blue = int(sqrt($blue));

print "sqrt colour <$col_item> red <$red> green <$green> blue <$blue>\
+n";

}

MainLoop;
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