Distribution · colour

Color::Scheme

Works

Rotate a Color's hue by a list of degree offsets and return the resulting colours, with seventeen named offset sets baked in.

Version: 1.001003 github:holli-holzer
Depends: Color
License: BSD-3-Clause
Its own test suite: 1 file, green
Checked: 2026-09-15 against Raku++ 3.28.0 and Rakudo 2026.08
Where it lives: raku.land · source

Install it #

$ rakupp install Color::Scheme

zef install Color::Scheme writes the same store; either installer leaves the module usable by both engines.

What it is for #

Picking a palette from a single brand colour is a solved problem in colour theory: the harmonies are fixed angular relationships on the hue wheel. Triadic is 120 degrees apart, tetradic is 90, split-complementary is 150 and 210, and so on.

This distribution knows seventeen of those relationships by name and applies them.

Generating a palette #

File

use Color;
use Color::Scheme;

my $base = Color.new('#1A3CFA');
say 'base : ', $base.to-string('hex');
say '';
for <triadic tetradic analogous split-complementary clash neutral> -> $name {
    my @p = color-scheme($base, $name);
    say sprintf('%-22s %d  %s', $name, @p.elems, @p.map(*.to-string('hex')).join(' '));
}

Output

base : #1A3CFA

triadic                3  #1A3CFA #FA1A3C #3CFA1A
tetradic               4  #1A3CFA #FA1AAC #FAD81A #1AFA68
analogous              6  #1A3CFA #681AFA #D81AFA #FA1AAC #FA1A3C #FA681A
split-complementary    3  #1A3CFA #FA681A #1AD1FA
clash                  3  #1A3CFA #FA1AAC #1AFA68
neutral                6  #1A3CFA #301AFA #681AFA #A01AFA #D81AFA #FA1AE4

The first colour of every palette is the base itself — the round trip through hue-saturation-value is lossless for these inputs, so palette[0] really is what you handed in.

Your own angles #

File

use Color;
use Color::Scheme;

my $base = Color.new('#FF0000');

say 'explicit [0, 180]  : ', color-scheme($base, [0, 180]).map(*.to-string('hex')).join(' ');
say 'explicit [0, 120, 240] : ',
    color-scheme($base, [0, 120, 240]).map(*.to-string('hex')).join(' ');
say '';
say 'angles wrap, and accept negatives and fractions:';
for 360, -120, 720, 12.5 -> $a {
    say sprintf('  %-6s -> %s', $a, color-scheme($base, [$a]).map(*.to-string('hex')).join);
}
say '';
say 'returns an ', color-scheme($base, [0, 180]).^name, ' of ',
    color-scheme($base, [0, 180])[0].^name;

Output

explicit [0, 180]  : #FF0000 #00FFFF
explicit [0, 120, 240] : #FF0000 #00FF00 #0000FF

angles wrap, and accept negatives and fractions:
  360    -> #FF0000
  -120   -> #0000FF
  720    -> #FF0000
  12.5   -> #FF3500

returns an Array of Color

The angles must be Real. A list of numeric strings is refused from inside Color.rotate with expected Real but got Str.

The seventeen names #

File

use Color::Scheme;

say Color::Scheme::color-scheme-angles.keys.sort.join("\n");

Output

analogous
clash
five-tone-a
five-tone-b
five-tone-cs
five-tone-ds
five-tone-es
four-tone-ccw
four-tone-cw
neutral
six-tone-ccw
six-tone-cw
split-complementary
split-complementary-ccw
split-complementary-cw
tetradic
triadic

Note the qualification. color-scheme-angles is our, not exported — so unqualified it is an undeclared routine on Rakudo. Write the full name.

The one thing to know #

:debug is not a logging flag. It writes a file into the current working directory.

File

use Color;
use Color::Scheme;

my $dir = $*TMPDIR.add("cs-{$*PID}");
$dir.mkdir;
LEAVE { .unlink for $dir.dir; $dir.rmdir }

indir $dir, {
    say 'files before : ', $dir.dir.map(*.basename).sort.join(' ') || '(none)';
    my @p = color-scheme(Color.new('#1A3CFA'), 'triadic', :debug);
    say 'palette      : ', @p.map(*.to-string('hex')).join(' ');
    say 'files after  : ', $dir.dir.map(*.basename).sort.join(' ');
    say '';
    my $f = $dir.add('colors.html');
    say 'the file holds a swatch per colour, plus four empty ones:';
    say '  empty background-color rules : ',
        $f.slurp.comb('background-color:;').elems;
}

Output

files before : (none)
palette      : #1A3CFA #FA1A3C #3CFA1A
files after  : colors.html

the file holds a swatch per colour, plus four empty ones:
  empty background-color rules : 4

colors.html is spurted into $*CWD with no path argument reaching the caller, no notice, and no regard for an existing file of that name. Worse, the generated HTML always indexes seven swatches regardless of how many colours the scheme has, under a quietly block — so a three-colour triadic scheme produces four empty background-color:; rules.

Do not leave :debug in anything that ships.

Where the two engines differ #

In the size of that debug file, by one byte per line: the module's own source has CRLF line endings, and Raku++ keeps the carriage return inside a multi-line quoted literal where Rakudo strips it. The palettes themselves are identical.

The other difference is about names rather than colours. Unqualified color-scheme-angles resolves on Raku++ and is a compile-time undeclared routine on Rakudo, so code developed against one engine fails to compile on the other. Qualify it.

One thing that is the same on both and worth knowing before you ship a palette: a greyscale base colour yields N identical colours. Hue rotation of a zero-saturation colour is a no-op, so #808080 triadic is three copies of #808080.

The distribution's metadata auth and the unit's own declared auth disagree, which is why the installer reports a different identity from the one on raku.land.