colorous palettes

colorous is a port of d3-scale-chromatic: well-known perceptual gradients (viridis, plasma, spectral, …) and categorical palettes (tableau10, set3, accent, …). Everything here returns opaque sRGB colors; use plt_convert if you need another space.

There are two kinds of name and two sets of functions:

Kind	Count	Functions
Continuous gradient	38	plt_colorous_gradient, plt_colorous_palette
Categorical palette	10	plt_colorous_categorical

Names are lowercase constant names from colorous, and matching is case-insensitive with - and spaces counting as _ ('Blue Green' = 'blue_green'). grey/gray spellings both work where colorous itself has them.

Gradients

plt_colorous_gradient(name, t)

Signature: plt_colorous_gradient(name VARCHAR, t DOUBLE) -> plt_color

One color from a gradient at position t in [0, 1]. Out-of-range positions are clamped, so -1 gives the start and 2 the end rather than an error.

SELECT plt_to_hex(plt_colorous_gradient('viridis', 0)) AS start,
       plt_to_hex(plt_colorous_gradient('viridis', 0.5)) AS middle,
       plt_to_hex(plt_colorous_gradient('viridis', 1)) AS end;

SELECT t, plt_to_hex(plt_colorous_gradient('spectral', t)) AS color
FROM (VALUES (0.0), (0.25), (0.5), (0.75), (1.0)) v(t);

t is continuous, so it works as a colormap for any numeric column:

SELECT value, plt_to_hex(plt_colorous_gradient('plasma', value / 100.0)) AS color
FROM (VALUES (10), (45), (80)) v(value);

plt_colorous_palette(name, n)

Signature: plt_colorous_palette(name VARCHAR, n BIGINT) -> plt_color[]

n colors sampled evenly across the gradient, from start to end. n must be at least 1; zero or a negative count is an error.

SELECT list_transform(plt_colorous_palette('viridis', 5), lambda x: plt_to_hex(x)) AS five,
       length(plt_colorous_palette('viridis', 5)) AS count;

This is the usual way to build a categorical scale out of a continuous one — pick as many colors as you have categories:

SELECT i, plt_to_hex(plt_colorous_palette('turbo', 4)[i]) AS color
FROM range(1, 5) t(i);

plt_colorous_palettes()

Signature: plt_colorous_palettes() -> VARCHAR[]

All 38 gradient names — sequential multi-hue (turbo, viridis, inferno, magma, plasma, cividis, warm, cool, cubehelix, blue_green, blue_purple, green_blue, orange_red, purple_blue_green, purple_blue, purple_red, red_purple, yellow_green_blue, yellow_green, yellow_orange_brown, yellow_orange_red), single-hue (blues, greens, greys, oranges, purples, reds), diverging (brown_green, pink_green, purple_green, purple_orange, red_blue, red_grey, red_yellow_blue, red_yellow_green, spectral) and cyclical (rainbow, sinebow).

SELECT list_count(plt_colorous_palettes()) AS count,
       plt_colorous_palettes() AS gradients;

Categorical palettes

plt_colorous_categorical(name)

Signature: plt_colorous_categorical(name VARCHAR) -> plt_color[]

A whole categorical palette. The length is fixed by the palette: 10 for category10 and tableau10, 12 for paired and set3, 9 for pastel1 and set1, and 8 for accent, dark2, pastel2 and set2:

SELECT list_transform(plt_colorous_categorical('tableau10'), lambda x: plt_to_hex(x)) AS tableau10;

SELECT name, length(plt_colorous_categorical(name)) AS colors
FROM unnest(plt_colorous_categoricals()) t(name);

plt_colorous_categoricals()

Signature: plt_colorous_categoricals() -> VARCHAR[]

The 10 categorical names: category10, accent, dark2, paired, pastel1, pastel2, set1, set2, set3, tableau10.

SELECT plt_colorous_categoricals() AS palettes;

Errors

An unknown name is a query error that points at the listing function:

SELECT plt_colorous_gradient('viridus', 0.5);

SELECT plt_colorous_categorical('tableau20');

SELECT plt_colorous_palette('viridis', 0);