Generate a rainbow color table with 256 entries as CSS

colortable256.pl

#!/usr/bin/perl

use POSIX;
use strict;

sub hsv2rgb {
    my ( $h, $s, $v ) = @_;

    if ( $s == 0 ) {
        return $v, $v, $v;
    }

    $h /= 60;
    my $i = floor( $h );
    my $f = $h - $i;
    my $p = $v * ( 1 - $s );
    my $q = $v * ( 1 - $s * $f );
    my $t = $v * ( 1 - $s * ( 1 - $f ) );

    if ( $i == 0 ) {
        return $v, $t, $p;
    }
    elsif ( $i == 1 ) {
        return $q, $v, $t;
    }
    elsif ( $i == 2 ) {
        return $p, $v, $t;
    }
    elsif ( $i == 3 ) {
        return $p, $q, $v;
    }
    elsif ( $i == 4 ) {
        return $t, $p, $v;
    }
    else {
        return $v, $p, $q;
    }
}

for (0..255) {
    my ($r, $g, $b) = map { floor($_ * 255) } hsv2rgb((255 - $_), 1, 1);
    print ".v$_ { background-color: ";
    printf("#%02x%02x%02x", $r, $g, $b);
    print "; }\n";
}