Solid reactive effects will pulse RGB light on key presses with user configurable hues. To enable gradient mode that will automatically change reactive color, add the following define:
```c
#define RGB_MATRIX_SOLID_REACTIVE_GRADIENT_MODE
```
Gradient mode will loop through the color wheel hues over time and its duration can be controlled with the effect speed keycodes (`RGB_SPI`/`RGB_SPD`).
By setting `RGB_MATRIX_CUSTOM_USER = yes` in `rules.mk`, new effects can be defined directly from your keymap or userspace, without having to edit any QMK core files. To declare new effects, create a `rgb_matrix_user.inc` file in the user keymap directory or userspace folder.