#include "FastLED.h"

#define NUM_LEDS 4
#define DATA_PIN 6
#define CLOCK_PIN 7

CRGB leds[NUM_LEDS];
unsigned char i = 0;

void setup() { 
  FastLED.addLeds<APA102, DATA_PIN, CLOCK_PIN>(leds, NUM_LEDS); 
}

void loop() { 
  leds[i] = CRGB::White; 
  FastLED.show(); 
  delay(300); 
  leds[i] = CRGB::Black; 
  FastLED.show();
  i++;
  i = i % 4;
}