Update: D'oh, I missed the "Websafe" requirement (people still worry about that?) -- Feel free to ignore me...

I have code which does this using Color::Calc.

# Example usage:
say for colors(distribute => 1, format=> "hex", n => 10, colors => [qw
+/red yellow green/]);



=head3 colors

At the most basic level, converts colors to different formats, however
+ this
subroutine is capable of quite a bit more than that.

Examples:

 colors [qw/red green blue/], format => "ps";
 colors [qw/red green blue/], format => "ps", n => 2;

=over 4

=item colors

A list of colors, can be an X11 color name or any of the other formats
recognised by Color::Calc.

=item n

Only return n colors.

=item interpolate

If false, requesting more colors than available in the colors list wil
+l
throw a fatal error. The default is to create new colors between the g
+iven
colors if there are insufficient colors provided. The interpolate comm
+and
will also cause colors to be interpolated if the distribute option is 
+set.

=item distribute

By default, if fewer colors are requested than are contained in the co
+lors
list, this subroutine will select the first n colors. Providing a true
value for distribute will cause the subroutine to evenly spread out th
+e
choice of colors over the range of colors provided (if n E<gt> 2 then 
+the
first and last colors are guaranteed to be included).

=item format

Specify the style of the returned colors. Can be anything supported by
Color::Calc which is currently (Color::Calc::VERSION == 1.0): "tuple",
"hex", "html", "object" (a Graphics::ColorObject object), "pdf". The
default format is "object".

The following formats are also accepted and are handled by this subrou
+tine
directly: "ps" | "postscript".

=item background

Try to make the colors appear on the given background color. Colors B<
+will>
be altered if this option is provided.

=back

=cut

#BEGIN: colors
sub colors {
  require Color::Calc;
  unshift @_, "colors" if @_ % 2;
  my %o = @_;
  my $c = $o{colors};
  my $n = $o{n} ||= @$c;
  $o{interpolate} = 1 unless exists $o{interpolate};
  croak "Not enough "."colors in plot color database" unless $o{interp
+olate} or $n <= @$c;

  $o{format} ||= 'object';
  $o{format}   = lc $o{format};

  @o{qw/format _format/} = qw/tuple ps/ if $o{format} =~ /^(?:ps|posts
+cript)$/;
  my $cct = Color::Calc->new( 'ColorScheme' => 'X', OutputFormat => 't
+uple' );
  my $cc  = Color::Calc->new( 'ColorScheme' => 'X', OutputFormat => $o
+{format} );

  $o{listed} = 1 if $o{format} eq 'tuple';

  if (($n > @$c) or ($o{distribute} and $o{interpolate})) {
    $c = [map [($_==int($_))?$$c[$_]:$cct->mix($$c[int $_],$$c[int($_)
++1], $_-int($_))], map +($_*($#{$c})/(($n-1)||1)), 0..$n-1];
  } elsif ($o{distribute} and $n < @$c) {
    $c = [map $$c[int($_*($#{$c})/(($n-1)||1))], 0..$n-1];
  }

  if ($o{background}) {
    my $fg = $cc->contrast_bw($o{background});
    if ($o{listed}) {
      $c = [ map [$cc->mix($_, $fg, .35)], @$c[0..$n-1] ];
    } else {
      $c = [ map $cc->mix($_, $fg, .35), @$c[0..$n-1] ];
    }
  } else {
    if ($o{listed}) {
      $c = [ map [$cc->get($_)], @$c[0..$n-1] ];
    } else {
      $c = [ map $cc->get($_), @$c[0..$n-1] ];
    }
  }

  if ($o{_format}) {
    $o{_format} eq 'ps' and do { for (@$c) { $_ /= 255 for @$_ } };
  }

  return wantarray ? @$c : $c;
}
#END: colors
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