---
title: RGB Underglow Configuration
sidebar_label: RGB Underglow
---

See the [RGB Underglow feature page](../features/underglow.md) for more details, including instructions for adding underglow support to a board.

See [Configuration Overview](index.md) for instructions on how to change these settings.

## Kconfig

RGB underglow depends on [Zephyr's LED strip driver](https://github.com/zephyrproject-rtos/zephyr/tree/main/drivers/led_strip), which provides additional Kconfig options.

Definition file: [zmk/app/Kconfig](https://github.com/zmkfirmware/zmk/blob/main/app/Kconfig)

| Config                               | Type | Description                                           | Default |
| ------------------------------------ | ---- | ----------------------------------------------------- | ------- |
| `CONFIG_ZMK_RGB_UNDERGLOW`           | bool | Enable RGB underglow                                  | n       |
| `CONFIG_ZMK_RGB_UNDERGLOW_EXT_POWER` | bool | Underglow toggling also controls external power       | y       |
| `CONFIG_ZMK_RGB_UNDERGLOW_HUE_STEP`  | int  | Hue step in degrees (0-359) used by RGB actions       | 10      |
| `CONFIG_ZMK_RGB_UNDERGLOW_SAT_STEP`  | int  | Saturation step in percent used by RGB actions        | 10      |
| `CONFIG_ZMK_RGB_UNDERGLOW_BRT_STEP`  | int  | Brightness step in percent used by RGB actions        | 10      |
| `CONFIG_ZMK_RGB_UNDERGLOW_HUE_START` | int  | Default hue in degrees (0-359)                        | 0       |
| `CONFIG_ZMK_RGB_UNDERGLOW_SAT_START` | int  | Default saturation percent (0-100)                    | 100     |
| `CONFIG_ZMK_RGB_UNDERGLOW_BRT_START` | int  | Default brightness in percent (0-100)                 | 100     |
| `CONFIG_ZMK_RGB_UNDERGLOW_SPD_START` | int  | Default effect speed (1-5)                            | 3       |
| `CONFIG_ZMK_RGB_UNDERGLOW_EFF_START` | int  | Default effect index from the effect list (see below) | 0       |
| `CONFIG_ZMK_RGB_UNDERGLOW_ON_START`  | bool | Default on state                                      | y       |

Values for `CONFIG_ZMK_RGB_UNDERGLOW_EFF_START`:

| Value | Effect      |
| ----- | ----------- |
| 0     | Solid color |
| 1     | Breathe     |
| 2     | Spectrum    |
| 3     | Swirl       |

:::note
The `*_START` settings only determine the initial underglow state. Any changes you make with the [underglow behavior](../behaviors/underglow.md) are saved to flash after a one minute delay and will be used after that.
:::

## Devicetree

ZMK does not have any Devicetree properties of its own. See the Devicetree bindings for [Zephyr's LED strip drivers](https://github.com/zephyrproject-rtos/zephyr/tree/main/dts/bindings/led_strip).

See the [RGB underglow feature page](../features/underglow.md) for examples of the properties that must be set to enable underglow.