Color schemes

A scheme is a set of colors derived from one color by rotating its hue. All of these functions work inside the color's own space: an oklch input gives oklch results with the same lightness and chroma and a rotated hue, normalized into 0..360. Alpha is kept.

They need a space that carries a hue. Supported: hsl, hsv, hwb, hsluv, lch, lchuv, oklch, okhsl, okhsv, okhwb, the six partial CAM16 spaces cam16_jch, cam16_jmh, cam16_jsh, cam16_qch, cam16_qmh, cam16_qsh, and cam16_ucs_jmh. A space without a hue is rejected:

SELECT plt_complementary(plt_lab(50, 20, -30));

Converting first is the whole fix:

SELECT plt_to_hex(plt_complementary(plt_convert(plt_srgb(1, 0, 0), 'oklch'))) AS complement;

The functions return the scheme's other colors, in palette's order and not including the input color. All of them share the same list shape, so a query can treat them uniformly:

SELECT list_transform(plt_triadic(plt_oklch(0.6, 0.15, 30)), lambda x: plt_to_hex(x)) AS triadic;

plt_complementary(color)

Signature: plt_complementary(color plt_color) -> plt_color

The color opposite on the hue circle: hue + 180°. This one returns a single color rather than a list, because a complement is one color.

SELECT plt_to_hex(plt_complementary(plt_hsl(120, 1, 0.5))) AS complement,
       plt_components(plt_complementary(plt_hsl(120, 1, 0.5))) AS complement_hsl;

plt_split_complementary(color)

Signature: plt_split_complementary(color plt_color) -> plt_color[]

The two colors at hue + 150° and + 210° — the neighbors of the complement.

SELECT plt_components(plt_split_complementary(plt_hsl(120, 1, 0.5))[1]) AS first,
       plt_components(plt_split_complementary(plt_hsl(120, 1, 0.5))[2]) AS second;

plt_analogous(color)

Signature: plt_analogous(color plt_color) -> plt_color[]

The two colors at hue − 30° and + 30°.

SELECT list_transform(plt_analogous(plt_hsl(120, 1, 0.5)), lambda x: plt_to_hex(x)) AS analogous;

plt_analogous_secondary(color)

Signature: plt_analogous_secondary(color plt_color) -> plt_color[]

The next pair out, at hue − 60° and + 60°. Together with plt_analogous this gives the five-color analogous scheme.

SELECT plt_components(plt_analogous_secondary(plt_hsl(120, 1, 0.5))[1]) AS minus_60,
       plt_components(plt_analogous_secondary(plt_hsl(120, 1, 0.5))[2]) AS plus_60;

plt_triadic(color)

Signature: plt_triadic(color plt_color) -> plt_color[]

The two colors at hue + 120° and + 240°.

SELECT list_transform(plt_triadic(plt_hsl(120, 1, 0.5)), lambda x: plt_to_hex(x)) AS triadic;

plt_tetradic(color)

Signature: plt_tetradic(color plt_color) -> plt_color[]

The three colors at hue + 90°, + 180° and + 270° — the square scheme.

SELECT list_transform(plt_tetradic(plt_hsl(30, 1, 0.5)), lambda x: plt_to_hex(x)) AS tetradic;

plt_monochromatic(color, count)

Signature: plt_monochromatic(color plt_color, count INTEGER) -> plt_color[]

The odd one out: it keeps hue and saturation and cycles HSV value by 1/count from the current value, wrapping into 0..1. tinycolor's monochromatic. It returns exactly count colors and the first is the input color itself — unlike the hue schemes above, which leave the input out. count 0 gives an empty list and a negative count is an error. Results stay in the input space with the same alpha.

SELECT list_transform(plt_monochromatic(plt_srgb(1, 0, 0), 4),
                      lambda x: plt_to_hex(x)) AS reds,
       plt_components(plt_monochromatic(plt_hsl(120, 1, 0.5), 3)[2]) AS second_hsl;

plt_harmony(color, scheme)

Signature: plt_harmony(color plt_color, scheme VARCHAR) -> plt_color[]

The name-based entry point for all six schemes. It accepts the names in plt_color_schemes() plus the aliases complement, split_complement, triad and square. This is what you reach for when the scheme comes from a column or a parameter. The six schemes all rotate the hue, so monochromatic is not one of them — it varies HSV value instead and has its own function, above.

SELECT scheme,
       list_transform(plt_harmony(plt_oklch(0.6, 0.15, 30), scheme),
                      lambda x: plt_to_hex(x)) AS colors
FROM (VALUES ('complementary'), ('split_complementary'), ('analogous'),
             ('analogous_secondary'), ('triadic'), ('tetradic')) t(scheme);

SELECT plt_to_hex(plt_harmony(plt_oklch(0.6, 0.15, 30), 'Square')[1]) AS first_of_square;

SELECT plt_harmony(plt_oklch(0.6, 0.15, 30), 'bogus');

plt_color_schemes()

Signature: plt_color_schemes() -> VARCHAR[]

The six canonical scheme names: complementary, split_complementary, analogous, analogous_secondary, triadic, tetradic.

SELECT plt_color_schemes() AS schemes;