#include "FastLED.h"
#include <Wire.h>

#define NUM_LEDS 6
#define DATA_PIN 6
#define SLAVE_ADDRESS 0x12

// Define the array of leds
CRGB leds[NUM_LEDS];

void setup() { 
  FastLED.addLeds<NEOPIXEL, DATA_PIN>(leds, NUM_LEDS);
  Wire.begin(SLAVE_ADDRESS);
  Wire.onReceive(receiveData);
}

void loop() { 
  delay(500);
}

void receiveData(int byteCount) {
  while(Wire.available()) {
    if (1 == Wire.read()) {
      leds[0]   = CRGB::Red;
      FastLED.show();
    } else {
      leds[0] = CRGB::Blue;
      FastLED.show();
    }
  }
}