Try using the controller's built-in WS2812 RGB LED on GP23

keyboards/tutte_coxeter_36k/config.h

@@ -1 +1,6 @@
 #define LED_CAPS_LOCK_PIN GP25
+
+#define WS2812_DI_PIN GP23
+#define RGBLIGHT_LED_COUNT 1
+#define RGBLIGHT_DEFAULT_HUE 180
+#define RGBLIGHT_LAYERS

keyboards/tutte_coxeter_36k/keymaps/default/keymap.c

@@ -28,3 +28,52 @@ const uint16_t PROGMEM keymaps[][MATRIX_ROWS][MATRIX_COLS] = {
                                                 KC_DEL,             KC_TAB,             KC_SPC,    KC_ENT,   KC_ESC,             KC_BSPC
     )
 };
+
+// Light our single RGB LED blue when caps lock is active.
+const rgblight_segment_t PROGMEM my_capslock_layer[] = RGBLIGHT_LAYER_SEGMENTS(
+    {0, 1, HSV_BLUE}       // Light 1 LEDs, starting with LED 1
+);
+// Light our single RGB LED cyan when keyboard layer 0 is active
+const rgblight_segment_t PROGMEM my_layer0_layer[] = RGBLIGHT_LAYER_SEGMENTS(
+    {0, 1, HSV_CYAN}
+);
+// Light our single RGB LED red when keyboard layer 1 is active
+const rgblight_segment_t PROGMEM my_layer1_layer[] = RGBLIGHT_LAYER_SEGMENTS(
+    {0, 1, HSV_RED}
+);
+// Light our single RGB LED purple when keyboard layer 2 is active
+const rgblight_segment_t PROGMEM my_layer2_layer[] = RGBLIGHT_LAYER_SEGMENTS(
+    {0, 1, HSV_PURPLE}
+);
+// Light our single RGB LED green when keyboard layer 3 is active
+const rgblight_segment_t PROGMEM my_layer3_layer[] = RGBLIGHT_LAYER_SEGMENTS(
+    {0, 1, HSV_GREEN}
+);
+// etc...
+
+// Now define the array of layers. Later layers take precedence
+const rgblight_segment_t* const PROGMEM my_rgb_layers[] = RGBLIGHT_LAYERS_LIST(
+    my_capslock_layer,
+    my_layer1_layer,    // Overrides caps lock layer
+    my_layer2_layer,    // Overrides other layers
+    my_layer3_layer     // Overrides other layers
+);
+
+void keyboard_post_init_user(void) {
+    // Enable the LED layers
+    rgblight_layers = my_rgb_layers;
+}
+
+bool led_update_user(led_t led_state) {
+    rgblight_set_layer_state(0, led_state.caps_lock);
+    return true;
+}
+
+
+layer_state_t default_layer_state_set_user(layer_state_t state) {
+    // Light up based on the layer
+    rgblight_set_layer_state(2, layer_state_cmp(state, 1)); // Layer 1 active
+    rgblight_set_layer_state(3, layer_state_cmp(state, 2)); // Layer 2 active
+    rgblight_set_layer_state(4, layer_state_cmp(state, 3)); // Layer 3 active
+    return state;
+}

keyboards/tutte_coxeter_36k/keymaps/default/rules.mk

@@ -0,0 +1,2 @@
+RGBLIGHT_ENABLE = yes
+WS2812_DRIVER = vendor

keyboards/tutte_coxeter_36k/keymaps/vial/rules.mk

@@ -1,2 +1,5 @@
 VIA_ENABLE = yes
 VIAL_ENABLE = yes
+
+RGBLIGHT_ENABLE = yes
+WS2812_DRIVER = vendor