> For the complete documentation index, see [llms.txt](https://developers.felt.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://developers.felt.com/felt-style-language/colors-and-palettes.md).

# Colors & palettes

Colors appear throughout the Felt Style Language — in `paint` (`color`, `strokeColor`), in `label` (`color`, `haloColor`), and in legends. There are three ways to express a color:

1. **A literal color** — a hex, HSL, or RGB string.
2. **A smart color** — the keyword `"auto"`, which Felt resolves to a contrasting color at render time.
3. **A palette shortcut** — a named, multi-color ramp like `@galaxy`, used by data-driven (categorical, numeric, heatmap, H3) visualizations.

## Literal colors

Any of these string formats are accepted wherever a single color is expected:

```json
{
  "color": "#3B82F6",
  "strokeColor": "hsl(217, 80%, 40%)",
  "haloColor": "rgb(38, 113, 0)"
}
```

`rgba(...)` is also supported and is handy for fully-transparent fills (for example, a transparent "Other"/background class in a categorical raster: `"rgba(0, 0, 0, 0)"`).

## Smart color: `"auto"`

`"auto"` computes a contrasting color automatically, based on the current map theme and the colors around it. It keeps strokes and label halos legible without hard-coding a value that might clash on a dark basemap or against a particular fill.

Prefer `"auto"` for:

* `strokeColor` on points and polygons
* `color` and `haloColor` on labels

…unless a specific color has been requested.

```json
{
  "paint": {
    "color": "#8F7EBF",
    "strokeColor": "auto",
    "strokeWidth": 1
  },
  "label": {
    "color": "auto",
    "haloColor": "auto",
    "haloWidth": 1.5
  }
}
```

## Palette shortcuts

For any **data-driven** visualization, prefer a named palette over a hand-built color array. Palettes are referenced with an `@` prefix (for example `"color": "@galaxy"`) and Felt expands them to the right number of colors for your classes or categories.

{% hint style="info" %}
Only the palette names listed below are valid. Use **sequential** palettes for single-direction data (population, elevation), and **diverging** palettes for data with a meaningful midpoint (change from a baseline, temperature anomaly). Reserve literal hex/HSL colors for simple (uniform) styles or when a specific color is requested.

The families below are guidance, not rules: Felt doesn't check a palette against the visualization type, so any palette name works in any color property.
{% endhint %}

### Vector palettes

Used by categorical, numeric, heatmap, and H3 visualizations on points, lines, and polygons.

#### Sequential (low → high)

| Palette      | Description                    |
| ------------ | ------------------------------ |
| `@galaxy`    | Pale yellow-green to dark teal |
| `@ylRed`     | Yellow to red                  |
| `@ylGrn`     | Yellow to green                |
| `@purpYl`    | Yellow to purple               |
| `@pinkYl`    | Yellow to pink                 |
| `@lightning` | Lightning gradient             |
| `@copper`    | Copper gradient                |
| `@spruce`    | Spruce green                   |
| `@riverine`  | Water gradient                 |
| `@neptune`   | Blue gradient                  |
| `@violet`    | Violet gradient                |
| `@purple`    | Purple gradient                |

#### Diverging (two directions from a center)

| Palette   | Description                      |
| --------- | -------------------------------- |
| `@bluRd`  | Blue to red                      |
| `@tealOr` | Teal to orange (colorblind-safe) |
| `@bluBr`  | Blue to brown                    |
| `@grnOr`  | Green to orange                  |
| `@purGrn` | Purple to green                  |
| `@weath`  | Weather gradient                 |

#### Categorical (distinct colors)

| Palette                         | Description                    |
| ------------------------------- | ------------------------------ |
| `@catPalette1` … `@catPalette7` | Categorical color schemes      |
| `@catPalettePT1`                | Paul Tol categorical palette 1 |
| `@catPalettePT2`                | Paul Tol categorical palette 2 |

Sequential and diverging vector palettes also come in numbered variants that request a specific number of colors — for example `@galaxy7`, `@galaxy8`, `@galaxy9`. Every sequential and diverging vector palette has variants for 2 through 9 colors. The unnumbered name lets Felt pick the right count for you, which is usually what you want.

### Heatmap palettes

Used by `heatmap` visualizations, ordered from least to most density.

| Palette          | Description                                |
| ---------------- | ------------------------------------------ |
| `@geyser`        | Green → beige → orange → red               |
| `@redOrHeat`     | Yellow → orange → red → magenta            |
| `@purpYlHeat`    | Light yellow → coral → pink → purple       |
| `@lightningHeat` | Purple → teal → green → yellow             |
| `@ylGrnHeat`     | Dark teal → green → yellow                 |
| `@bluRdHeat`     | Blue → gray → red (diverging feel)         |
| `@tealRedHeat`   | Teal → green → yellow → orange → pink      |
| `@purpYlPink`    | Purple → teal → yellow → orange → red/pink |

### Raster palettes

Used by numeric, hillshade, and raster-algebra visualizations.

#### Sequential

| Palette          | Description                                                                           |
| ---------------- | ------------------------------------------------------------------------------------- |
| `@feltGrays`     | Grayscale gradient                                                                    |
| `@cbBlues`       | ColorBrewer blues                                                                     |
| `@cbPurples`     | ColorBrewer purples                                                                   |
| `@feltPinks`     | Pink gradient                                                                         |
| `@cmOceanGreens` | Ocean greens gradient                                                                 |
| `@pattFeltOcean` | Teal ocean gradient                                                                   |
| `@cmOceanDeep`   | Deep ocean gradient                                                                   |
| `@mpaInferno`    | Matplotlib inferno — note the spelling: `mpa`, not `mpl`                              |
| `@mplPlasma`     | Matplotlib plasma                                                                     |
| `@mplVirdis`     | Matplotlib viridis, perceptually uniform — note the spelling: `Virdis`, not `Viridis` |
| `@cividis`       | Cividis — colorblind-safe                                                             |
| `@feltYlRed`     | Felt red to yellow                                                                    |
| `@veg`           | Vegetation gradient                                                                   |

#### Diverging

| Palette        | Description                            |
| -------------- | -------------------------------------- |
| `@feltWeath`   | Felt weather gradient                  |
| `@feltHeat`    | Felt heat gradient                     |
| `@feltVibrant` | Felt vibrant gradient                  |
| `@nclBlOrRed`  | NCL blue-orange-red diverging          |
| `@cbRedYlGrn`  | ColorBrewer red-yellow-green diverging |
| `@cbBrBG`      | ColorBrewer brown-blue-green diverging |

#### Terrain

| Palette        | Description                |
| -------------- | -------------------------- |
| `@terrain`     | Terrain elevation gradient |
| `@rTerrain`    | R terrain gradient         |
| `@feltHypso`   | Felt hypsometric tints     |
| `@wikiTerrain` | Wikipedia terrain gradient |

#### Vegetation

| Palette     | Description                |
| ----------- | -------------------------- |
| `@nasaNDVI` | NASA NDVI vegetation index |

For raster **categorical** layers, use the vector categorical palettes above (`@catPalette1` … `@catPalette7`, `@catPalettePT1`, `@catPalettePT2`).

Raster palettes also support numbered variants to request a specific number of steps — for example `@feltGrays2`, `@feltGrays3`, … `@feltGrays9`.

## How colors map to classes

When a palette or color array drives a data-driven visualization, the number of colors should line up with the number of classes or categories:

* **Categorical:** one color per category. With `showOther: true` and an explicit `categories` array, provide **N + 1** colors — the extra one styles the "Other" bucket.
* **Classed numeric:** **N break points produce N − 1 classes**, so an explicit color array needs N − 1 entries.
* **Continuous:** provide **2 or more** colors and Felt interpolates smoothly between them in the [HCL color space](https://en.wikipedia.org/wiki/HCL_color_space).

A palette shortcut handles all of this for you — Felt expands `@galaxy` to exactly the colors it needs. Reach for explicit arrays only when you want precise control over each color.


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