QMK Dynamic Layer Lighting

config.h

/* (Optional) Define RGB settings in your config.h */ 
#ifdef RGBLIGHT_ENABLE
#    define RGBLIGHT_ANIMATIONS
#    define RGBLIGHT_HUE_STEP 8
#    define RGBLIGHT_SAT_STEP 8
#    define RGBLIGHT_VAL_STEP 8
#    define RGBLIGHT_LIMIT_VAL 150
#    define RGBLIGHT_SLEEP
// #    define RGBLIGHT_LAYERS  // We do NOT need the layers!
#endif

keymap.c

/* Enable dynamic layer lighting.
 *   - Changes hue based on your current color.
 *   - Uses your current saturation and brigtness settings.
 */

/* Add these declarations to the top of your keymap.c
 */

#ifdef RGBLIGHT_ENABLE
static rgblight_config_t home_rgb;

void set_rgb_home(void);
void set_rgb_by_layer(layer_state_t);
#endif

/* Be sure to add the following keycodes to your map!
 * "Adjust" is a good layer choice.
 *  - RGB_SAI,
 *  - RGB_HUI,
 *  - RGB_VAI
 */

/* Add the rgb blocks to the following functions
 *  - keyboard_post_init
 *  - layer_state_set_user
 *  - process_record_user
 */

void keyboard_post_init_user(void) {
    // Call the keymap level matrix init.

#ifdef RGBLIGHT_ENABLE
    set_rgb_home();
#endif
}

layer_state_t layer_state_set_user(layer_state_t state) {
#ifdef RGBLIGHT_ENABLE
    set_rgb_by_layer(state);
#endif
}

void post_process_record_user(uint16_t keycode, keyrecord_t *record) {
    // Regular user keycode case statement
    switch (keycode) {
#ifdef RGBLIGHT_ENABLE
        case RGB_HUD:
        case RGB_HUI:
        case RGB_SAD:
        case RGB_SAI:
        case RGB_VAD:
        case RGB_VAI:
            set_rgb_home();
            break;
#endif
        default:
            break;
    }
}

/* Somewhere near the end of your keymap.c
 *
 * This block sets up the layer state and colors.
 */

#ifdef RGBLIGHT_ENABLE

void set_rgb_home(void) {
    home_rgb.raw = eeconfig_read_rgblight();
}

void set_rgb_by_layer(layer_state_t state) {
    if (!rgblight_is_enabled()) {
        return;  // lighting not enabled
    }

    uint8_t offset = 0;
    switch (get_highest_layer(state)) {
        case _RAISE:
            offset = 2 * RGBLIGHT_HUE_STEP;
            break;
        case _LOWER:
            offset = -2 * RGBLIGHT_HUE_STEP;
            break;
        case _NAV:
            offset = 1 * RGBLIGHT_HUE_STEP;
            break;
        // case _ADJUST:  // layer color not recommended on layer w/ rgb keys
        //     offset = -96;
        //     break;
        default:  //  for any other layers, or the default layer
            break;
    }
    rgblight_sethsv_noeeprom((home_rgb.hue + offset) % 255, home_rgb.sat, home_rgb.val);
}
}

#endif

rules.mk

/* Turn on RGB underglow */
RGBLIGHT_ENABLE = yes      # Enable keyboard RGB underglow